You couldn't make it up: behind the scenes on Twenty Twelve

Gerard Gilbert is granted an exclusive guided tour behind the scenes of the award-winning comedy 'Twenty Twelve' – and discovers how sometimes life imitates art more closely than you imagine...

Visiting television drama and comedy sets can be a tedious business, with a lot of hanging around between takes and re-takes, but watching the first of the final three episodes of Twenty Twelve being filmed is a delight. I'm an admirer, anyway, of John Morton's award-winning BBC2 comedy about the Olympic Deliverance Commission (ODC), the fictional body tasked with organising the 2012 London Olympic Games, and this was like having a private live performance. And who cares about re-takes when a fantastic cast led by Hugh Bonneville, Jessica Hynes and Amelia Bullmore are delivering the sort of nuanced dialogue that almost demands repeat listening? Take five? Bring it on.

"You really do have to concentrate on the lines," says Bullmore, who plays Kay Hope, the head of sustainability, a role in charge of what happens to the Olympic venues after the Games. "It's speedy and feather-light; you don't sit on anything, you just bomb on through. If I had a fiver for every time John [Morton] said, 'Pace', I'd have a lot of fivers."

We're sitting in standard-issue partitioned offices on the 37th floor of the Canary Wharf Tower in London's Docklands – the previous series were filmed on the 29th floor, so this is a sitcom literally going up in the world – the windows affording a distant panoramic view of Olympic Park. As his character Ian Fletcher, ODC's head of deliverance, chairs a breakfast meeting to sort out the travel arrangements for visiting American VIPs, Hugh Bonneville is experiencing hiccups with his lines. "Obviously we can't have the First Lady sitting in traffic on the Balls Pond Road as Usain Bolt crosses the finishing line in the 100 metres," he recites smoothly after a couple of takes. "At the same time, we can't have Boris being mown down on his bike by a cavalcade of armour-plated Lincoln Continentals."

Not only is this a fiendishly intricate line to deliver in the midst of a rapid-fire ensemble scene, it's also very funny. Is Bonneville ever not able to retain a deadpan face? "You don't actually have time for corpsing because you're just panicking like hell to get it right," he says. "That scene took five hours and the challenge is to make it look effortless and accidental, but as you saw, it's actually very finely honed."

Bonneville is "zooming up and down the M4"to fit this filming into his ongoing commitments for Downton Abbey – his busy timetable one of the main reasons that this final series of Twenty Twelve was split in two; the first five episodes (screened in March) were filmed last summer, while this concluding trilogy has been left until nearly the last minute. "Trying to prise Hugh out of the arms of Downton Abbey is very tricky," says Morton, creator, writer and director of the series. "The good consequence of that is that I was able to leave three episodes to write closer to the Games, although actually they're not really fantastically topical. It's not like a stand-up doing a routine about this week's news about the Olympics. It's trying to make up things that haven't happened but you feel might have."

Indeed, Twenty Twelve has become renowned for its almost spooky prescience, going right back to the very first episode in March 2011, which featured problems with the 1,000-day countdown clock. The morning after the episode aired, the real-life clock in Trafalgar Square broke down. "I had no idea there was a countdown clock," claims Morton, "and then to find out that not only had they done a clock but... it's just a wonderful piece of happenstance."

Others might suspect espionage – but Morton denies he had a mole inside the offices of the real-life version of ODC, the almost satirically named Locog (the London Organising Committee of the Olympic and Paralympic Games), which happens to have its headquarters a few floors down from the Twenty Twelve set. "There was someone in the costume department whose sister, I think, may have had occasion to go in [to Locog] and was able to give us a steer as to whether or not they wore ties," says Morton, "but I didn't want an inside track. These people are made up. I wanted to put some clear blue water between us and Locog."

He did, however, arrange a breakfast screening with the real-life Olympic organisers. "There was a bit of nervousness at the start and I said to them, 'I don't have a mole in your camp, so please relax.' They've been extremely helpful and I take that as a compliment, [although] there are people who have said, 'That's a measure of the fact that you haven't been satirical enough.' But then it's not a satire that takes pleasure in lining up a target and shooting it down... it's not the pure sort of Jonsonian satire of a bunch of nasty, venal people getting their just deserts... it's much kinder. And the fact that Seb Coe's been in it a few times and felt it was safe to do so... I thought it meant at least he recognised that it wasn't a demolition job."

Sebastian Coe, the chairman of Locog, was too busy to guest in the new trilogy of episodes, while Boris Johnson was otherwise engaged fighting May's London mayoral election. "We asked early on if he would be interested in doing a little piece and at that point the answer was no because of the elections," says Morton, "but when we were actually filming, it was post his re-election. Maybe he doesn't want to be associated with comedy these days, I don't know."

Instead, in scenes filmed outside Johnson's office at City Hall on London's South Bank, Paralympian-turned-politician Baroness Tanni Grey-Thompson plays herself, while Aled Jones also guest-stars, judging a bell-ringing competition. "I think we might have enquired about Cliff Richard, but he was too busy rehearsing the Jubilee Concert," says Morton. "And I think we might have enquired about Engelbert Humperdinck..."

The guests add a pleasing touch of verisimilitude to Twenty Twelve, but are tangential to the real meat of the show, which is a team of well-drawn characters inhabited by a fantastic cast. "The first time I looked at a monitor when we were shooting the first scene, I thought, 'God, how did we get these people to agree to do this and why are they prepared to work so hard?'" says Morton. "We have so little time to do it, and there are a lot of words in the script and they have to look as though they're not written. The precision they have to bring to it to make it look like it's not precise is... I'm eternally grateful."

In the final three episodes, Bonneville's Fletcher is still trying to marshal his incompetent team while waiting for his divorce to come through. "Hugh Bonneville is brilliant," says Morton. "He's a bright character surrounded by people talking utter nonsense, a straight man in a ship of fools, and Hugh does this thing between the lines: every time when you cut to him looking back at someone talking to him, there's something happening behind the eyes that is very funny. He'll look back at Jessica Hynes talking to him and as a viewer he lets you in on what he's thinking."

Hynes plays perhaps the most memorable character in Twenty Twelve, head of brand (and owner of horribly plausible PR company Perfect Curve) Siobhan Sharpe, who is prone to interjecting meaningless, vaguely food-related metaphors such as, "If you get bandwidth on this, you've got syrup on your waffle from word get-go," and "Guys, guys, we're chewing sourdough here, so pull out."

"I thought it was funny to have someone who thought she was American but came from Harpenden," says Morton. "I have met lots of people who've said, 'I know someone just like her.' It's quite worrying that there are real people out there like that, although I have met people who don't listen, and that's what she is – she doesn't listen... ever."

"The voice is very deadpan," says Hynes, who is scarily brilliant in the role. "Her killer instinct comes from one place, her glassy look from somewhere else – it's just an amalgam of people I've known over the years. People recognise her in all types of businesses because there's always someone who's a bit like her."

The slogan for the Olympics travel advice pack that Sharpe and Perfect Curve come up is "Way to Go", which, in this week's opening episode, leads to some hilarious exchanges about ways of improving London's traffic flow during the Games – such as banning pedestrians from pavements and turning them into dedicated cycle lanes ("Half the cyclists in London use the pavements anyway," observes head of infrastructure Graham Hitchens, played by Russell Brand's one-time comedy partner, Karl Theobald). Meanwhile, Kay Hope, trying to look beyond the tangled West Ham United-Tottenham Hotspur rival bids for the post-Games Olympic Stadium, approaches Football League Two club Dagenham & Redbridge.

Morton says he has tried not to be too obvious with the problems faced by the ODC. "I mean, there is a run of jokes about ticketing in the show but I never did a whole episode about ticketing because it's, well, out there in the press. I'm looking for small details, such as this guy who was caught doctoring Olympic starting pistols to fire live rounds – and that's true, there was a guy caught doing that, and they then made it illegal to own that type of starting pistol and brought in a new one that was a different colour. So that was a little news story that didn't go anywhere. In fact it wasn't a big security problem, but I thought that smells like an interesting thing to pick up and run with."

Generally, though, Morton thinks the office dynamics of Twenty Twelve could fit almost any large-scale organisation. "When you're younger you think everyone at the top level knows what they're doing," says Morton, "but then it begins to dawn on you that perhaps they don't. I remember [former England manager] Graham Taylor once allowed cameras to follow him, which was the greatest mistake he ever made. The top level of football was like any other Sunday afternoon kick-around... it was absolute chaos, and you start to think that maybe that's true of other things – politics or big corporations.

"You start with very laudable public aspirations around sustainability and legacy – and then work backwards towards the detail, and that's where the comedy seems to be. When it comes down to the day-to-day stuff, it's about the ratio of toilets to athletes. It's this gap that people are constantly stubbing their toes on."

As for plans for a spin-off, Morton simply can't envisage a public event that comes with the same magnitude or degree of jeopardy as the Olympic Games. "There's been some talk about whether there can be a life [for the series] post-Olympics and it's tempting because I'd love to work with those actors again. But I think the smart and the brave thing to do is to end it here."

In real life, Bonneville managed to buy some tickets for the Games, "legitimately through the ballot – if it had all gone wrong I would have had to sell my house because I'd spread my bets," he says. "But I probably won't be able to go because I'm filming Downton." And although he doesn't envisage any sort of spin-off sitcom, he can see how the characters from Twenty Twelve might continue their illustrious careers. "I've always thought that having assembled a crack team like this they could move into any big public organisation that needs assessment and help," he says. "So I'm pretty confident we could go and sort out the NHS, or the armed forces, or maybe even the banking system. That would be a good challenge..."

'Twenty Twelve' returns to BBC2 on Tuesday at 10pm