These past few weeks I’ve experienced what it must be like to be a Labour MP. Watching Tony Blair’s long drawn out departure, I’m torn between disagreeing with most of what he says while at the same time acknowledging that he has kept me in work for 10 years.

As the weeks pass, though, waiting for Blair’s exit has been a little like waiting for summer. We keep thinking it’s arrived only to turn on the television and see yet more evidence that it hasn’t.

At least Major went quickly. Oh yes. “When the curtain falls, it’s time to get off the stage and that is what I propose to do,” he said in an uncharacteristically theatrical metaphor.

Ironically, the image is much better suited to his successor. Major never really did showbiz. Blair lives it, breathes it, milks it. All the more surprising, then, that his departure has been rather a case of the performer desperately trying to stop the curtain from falling while he works on a grand finale.

This wasn’t how it was meant to end. Looking back at my first attempts at Blair for tomorrow night’s Channel 4 special, I was struck by the feeling of optimism that suffused those early programmes, even amid the satirical references to nepotism and peerages for favours.

My first Blair impression (1994) was all popping-out eyes and manic grin: part Michael Grade, part Bruce Forsyth. I hadn’t got him right, back then, but nor had he; and for the next 13 years it was a competition between the two of us as to who did the most manic Blair impression.

I don’t know how much I’ve turned into him or he’s turned into me. Either way, we’ve both been overtaken by David Cameron. I just copy Blair’s speech and mannerisms: Cameron does the whole career.

Listening to the Tory leader now, I hear Blair then. (“Future”, “Challenges”, “Changing the party to change the country”).

“You were the future once,” Cameron teased Blair at his first encounter across the dispatch box. Judging by Cameron’s language, he may well be the future again.

Language was all we had to go on in the early days, with Blair’s odd, verbless sentences and singsong delivery (“Tea for two. Of course, of course, tea for two. But also two for tea”). Even then it always sounded a little insincere. But, to give him credit, he worked at it and now, 10 years on, he sounds totally insincere.

Yet for so much of that time we believed him. Rather like watching David Blaine, for years we watched Blair and marvelled at his magic, even though we knew deep down that it was an illusion.

On Africa, on climate change, on Iraq, his act, like Blaine’s, depended on the fact that we wanted to believe it was true. And Blair wanted it to be true as well. It was, for him, technically impossible to tell a lie, as he believed everything he said to be true at the time that he said it.

The early sketches were mostly a variation of the “all-things-to-all-men” caricature. It was only later in the first term – after the “forces of conservatism” speech and the foot and mouth crisis had alienated many of the moderate Conservatives whose conversion won Labour the 1997 election – that we homed in on the Blair/Campbell relationship as being the key to the whole administration. What surprised us was the effect it had.

The actor Andy Dunn – who played Alastair Campbell – and I were essentially improvising around whatever information or research we had at our disposal, including an early colour supplement photo-reportage showing Blair and his team in shirtsleeves, sitting on sofas and shooting the breeze. Only later did we learn that the press office thought we had a mole in Downing Street.

We were often accused of attacking the man and not the ball: but this was a man who never passed the ball. Time after time he identified the government’s interests with his own, speaking of the “scars on my back”, his “irreducible core”, his lack of a reverse gear – and even telling the Hutton inquiry that the BBC’s allegations against him “went, in a sense, to the credibility, I felt, of the country”.

It’s ironic that this was the man who attacked Margaret Thatcher’s policies as being “the product of an unchecked and unbalanced mind . . . [that] came to confuse the notion of knowing your own mind with refusing to listen to anyone else”.

To me, Blair has always been the girl with the curl in the nursery rhyme: when he’s good, he’s very, very good. But when he’s bad, he’s horrid.

History will judge him, he says. And it will. But not before he and Campbell and Peter Mandelson and the rest have had a damn good go at rewriting it.

Tony Blair: My Part in His Downfall is on Channel 4 tomorrow at 11.05pm

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