As the executive producer on the series, I'm responsible for every aspect of the production - from liaising with the celebrities taking part, to overseeing the research for each episode, to approving scripts, to viewing the programmes as they're being put together in an edit suite.

The great thing about WDYTYA is that every episode is completely different - and when we start researching stories, we literally have no idea what we might unearth.

JK Rowling, who features in the second episode of Who Do You Think You Are?

In fact, it's finding a crucial document or a fantastic eyewitness that makes the job as brilliant as it is.

WDYTYA is now in its eighth series so this year we were determined to make the casting feel fresh and new. I'm hugely proud of this year's line-up and hope you're all excited about some of the names coming up over the next 10 weeks.

I'm really pleased to have our very first artist, Tracey Emin, and our first author - probably the most successful living author in the world, JK Rowling - for this year's series.

And the rest of the cast is a roll call of familiar names, whether that's because of the music they've made, like Robin Gibb from The Bee Gees, or because of their performances on some of the BBC's biggest shows, like Len Goodman from Strictly Come Dancing, and Emilia Fox.

Casting the series is always a really exciting part of the process. We're exceptionally lucky that lots of people really want to explore their family history - and often people come to us with something particular they'd like to discover.

The hard part comes when the research begins.

Before we commit to making an episode with a particular celebrity, we do around three months of dedicated research - first building their family tree, then trying to get all the documents available relating to their ancestors.

This is a painstaking task, which often leads to dead ends and brick walls.

Sometimes, we're extremely lucky - a vital clue will simply fall into our hands. But in some cases we have to make the difficult decision to stop the research and let the celebrity know that we won't be able to make the programme.

Of course, we provide them with all the research we've accumulated - but as far as the series goes, that's the end of the story.

This means for a run of 10 episodes, we research around 30 people.

This year's series launches with June Brown - a British television icon, but also the oldest person to take part in the series.

I have to say, though, that at 84 June has remarkable energy, boundless goodwill and a really naughty sense of humour.

Usually, the participants go on the journey alone, with just the crew and the director for company. June was accompanied by one of her daughters, so it really was a family adventure.

June's journey takes her from London to Holland to Spain - and she never flagged. I think she was fortified by her cigarettes - she smokes almost as many as her character Dot Branning in EastEnders.

WDYTYA can be very emotional for the celebrities taking part.

Emilia Fox was eight months pregnant when we filmed her episode and we knew that one of the stories she would encounter involved a stillbirth for one of her ancestors. We were hugely aware of how emotional - and difficult - this might be for Emilia.

Though we don't reveal anything about what's coming up to those taking part, we do always warn everyone that history has a habit of taking surprising twists and turns - and that they might not always like what they find.

The directors on the series are all hugely experienced and are especially good at dealing with these very raw situations. We never shy away from an emotional reaction, but we always make sure it's not mawkish or sensationalised.

There is a major revelation in JK Rowling's film, which could have caused her and her family considerable discomfort.

I discussed this particular revelation - and the way in which it would be revealed to Jo - with the director and series producer many, many times in the months leading up to filming.

We decided in the end that it had to be as real as possible - after all, it's Jo's journey and not ours.

We're really proud of the resulting scene, and the rest of the film, so it would be great to hear what everyone else thinks. It's certainly a heart-stopping moment and one I'll always remember from my time on the series.

Perhaps the most difficult experience I've had on the series was during last year's run when our research team discovered that Alan Cumming's maternal grandfather had accidentally killed himself playing a game of Russian Roulette.

Alan's family weren't aware of this - knowing only that he'd died in a "shooting incident".

We, as a team, felt an enormous responsibility to Alan and his mum, but we also knew that they really wanted to know the truth.

The moment of discovery for Alan was, I think, hugely shocking, disturbing and upsetting - but ultimately brought his family the knowledge they'd desperately craved.

Liz Dobson, who directed both Alan and Kim Catrall's WDYTYA, did a remarkable job. It could easily have been a very sensationalist film - but it's actually a celebration of Alan's grandfather's life.

Luckily, it's not always tears and tragedy. It's fantastic to feature stories of great triumph and heroism.

Larry Lamb's film this year is very special to me as we managed to unite Larry with a relative he never knew he had - on the other side of the world - and there's real humour in this year's series too.

Alan Carr brings a fantastic sense of fun to his episode - even when there's bad news, he just keeps laughing.

So, with 10 extraordinary stories which cover four centuries, three continents and a year of research, filming and editing, I can't wait to hear what you make of the new series - and for everyone to discover the secrets and revelations that we've had to keep to ourselves for the past year.

Tom McDonald is the executive producer of Who Do You Think You Are?

Comments made by writers on the BBC TV blog are their own opinions and not necessarily those of the BBC.

Our experiment will see six well-loved British famous faces - Lionel Blair, Sylvia Syms, Liz Smith, Dickie Bird, Kenneth Kendall, and Derek Jameson - go back to 1975 for just one week to see if it can make them young again.

When I first heard about the original experiment, and the BBC's plans to re-stage it, as the programme executive, I thought it all sounded completely mad and not necessarily in a good way.

I wasn't instantly convinced by the original experiment - it sounded too much like that 1980s film Cocoon to me - and I was concerned that if we re-staged it we'd simply find that the experiment didn't work, and would be embarrassing for everyone involved.

Two things changed my mind. Firstly, meeting with Professor Ellen Langer, who ran the original study. Her passionate belief that the way we age isn't inevitable and her certainty the experiment would work was hugely inspiring and enough to convince me that re-staging the experiment could change the way we all see ageing.

The second thing was reading that there are now more people in the UK over 80 than there are under 16 in Britain. Suddenly the idea of re-staging this experiment sounded much more than just fun, it somehow seemed completely urgent and absolutely necessary.

First, we had to decide which year we'd be sending our volunteers back to. We chose 1975 as we needed our volunteers to go back to their heyday and it was a year that many of the celebrities themselves brought up as personally important.

Nineteen seventy five was also an interesting year in the news, in culture and in sport. Margaret Thatcher was elected as the first female leader of the opposition and the Bay City Rollers were so big that crowds of hysterical girls could be found in every part of Britain (look out for a brilliant news piece on Rollermania in the first episode).

In sport Arthur Ashe became the first black man to get to the Wimbledon final and the first ever Cricket World Cup took place at Lords (and with Dickie Bird in the line up, this seemed particularly poignant).

A lot of our energies went into getting the look and feel of the house as historically accurate as possible. We also wanted the house to be as personal to our six volunteers as possible - we describe it in the show as "an Aladdin's cave of seventies-ness," which I think sums it up perfectly.

We needed plenty of space in the grounds to squeeze portacabins in so the massive production team on the series could be rigged up to computers, printers and the internet. We wanted it to be 1975 inside the house, but in order for the production to run smoothly it needed to be 2010 everywhere else.

Joanna Hilliard started to gently ask the celebrities to recall the things they most remembered about their homes in 1975: What did they have in their bedrooms? What colour were their walls? What photos would they have had up around their house? Were there any special mementoes which always took them back to that time?

We wanted the moment the volunteers saw their bedrooms for the first time to have a huge impact on them, so the researchers couldn't tell them why we were asking all these questions about decor and photos. We couched it all in terms of general research.

Joanna managed to strike it lucky in the case of all the volunteers - but most especially with Lionel Blair who had photographs of his actual 1975 bedroom. With that photograph, we managed to entirely replicate the wallpaper, carpet, furniture, even the bedding so it was a stunt double of Lionel's 1975 bedroom.

We were all so excited by the job that David did with Lionel's bedroom, which is why Lionel's reaction (you'll have seen it in the first episode) came as such a surprise to us - he hated his room!

Meanwhile, inspired by Habitat catalogues, design books and archive photos, art director David and his team transformed a suburban house into a living and breathing 1970s home.

Being inside it was breathtaking because the level of detail was so extraordinary. We'd always insisted that it couldn't feel like a set. Everything from the washing machine to the fridge to the curling tongs to the bedside lamps had to work - it was there to make the 1970s real.

There are too many moments on this series that were either hilarious, moving or simply completely bonkers to pinpoint one of them - but what will always stay with me is the sense about half way through filming that the experiment really was working.

The atmosphere in the house changed from being a slightly sad retreat for some very nice elderly celebrities into being a dynamic, living, breathing space where collectively everyone was living as their younger selves.

I'd always believed the key to the experiment would be the six volunteers enjoying one another's company and getting on together - and seeing the encouragement they all gave one another to either walk those extra steps or push themselves that little bit harder was inspirational.

I will never forget the moment that Derek Jameson managed to pull on his socks on his own (harder than it sounds) to the applause of Lionel Blair and Liz Smith - it's the spirit of that house that I'll never forget.

I will never be able to look at a shag-pile carpet or swirly wallpaper again without thinking of our 1975 house. I did try and nab a few pieces of the furniture at the end of the shoot (I do have a soft spot for 1970s dressers and dining tables), but I came home empty-handed.

Nearly all of the props in the house were hired from specialist companies to be sure the pieces really would have been in a 1975 house - we really didn't want to find out something we thought was 1970s turned out to be from the 1980s.

I hope when the series is on air that viewers will see that - other than the joy of some terrible clothes and gaudy furniture - there's nothing particularly special about 1975. What the experiment showed me is that we all have the potential to think differently about who we are and the way we live, regardless of our age.

And the reason I'll always feel hugely grateful to have taken part: hearing the volunteers as they left the experiment talking about how much hope it had given them for the future and how glad they were they'd taken part. You'll see these conversations in the final episode on Thursday.

Spending one week in 1975 hasn't changed my life on a day-to-day basis but if ever I think I can't do something or I have a problem that's insurmountable, I do try and remember the 88-year-old Liz Smith walking for the first time since her strokes 18 months ago without sticks. Inspiring, life-affirming, and a privilege to have been a part of.

Tom McDonald is the executive producer of The Young Ones.

The Young Ones starts at 9pm on Tuesday, 14 September on BBC One and BBC HD. For times of all episodes of the show, please visit the upcoming episodes page.