The excitement (mine) is mounting … Not quite to the peak of the day I trotted out in front of 72000 people at Old Trafford with Diego Maradona (I never talk about it as regulars know) and three other World Cup winners as team-mates … Nor even an excitement to match election days 1997, 2001 and 2005 … Perhaps it is more on a par with the excitement I felt on seeing my first volume of diaries go to Number 1, or on seeing my first novel published, or playing my bagpipes in front of 2000 people at last year’s St Andrew’s Day concert in Glasgow.

Cultural you see … Beneath the political hardnut veneer is a culture vulture who has just finished Ian McEwen’s latest novel, Sweet Tooth, which is so brilliant, and with such a wonderful twist, that I have gone back to start it all over again to work out why I never saw it coming. And alongside it I was reading (late to the party) Claire Tomalin’s splendid biography of Dickens. It didn’t make me want to read it again, but it did make me want to read more of her – and his – books.

So get to the frigging point, you cry … Why the excitement this Bank Holiday Monday? And the answer is that tomorrow is Tuesday, and on BBC1 at 9pm, a largely indifferent public will witness my professional acting debut. Yes professional. I was paid – modestly I think – to play myself in episode 3 (I am also mentioned in episode 4, he added proudly) of Jimmy McGovern’s latest dramas in the ACCUSED series he makes with his RSJ partners Sita Williams and Roxy Spencer.

They were kind enough to send me all four in the series to France, where I am currently spending my last day on holiday before coming back to be close to a telly for the ACTUAL screening, to await the inevitable calls from agents, moguls and Hollywood studios who, provided they don’t blink twice in quick succession, will witness the magnetic appeal, the natural acting talent, and want to launch me on my next career, Eric Cantona style.

The critics, unsurprisingly perhaps, have tended to focus more on the fantastic, and rather deeper performances, of transvestite Sean Bean, and in last week’s ‘Mo’s story,’ a stunning performance by Anne-Marie Duff. Tomorrow is Stephen’s story, just as stunning, really powerful, and if it will be a surprise to some to see me in there, it will be a bigger surprise I think to see what a good serious actor Scouse comic John Bishop happens to be, playing Stephen’s dad.

I will give nothing away of the plot, other than to say that Stephen is going through a lot of family-created mental anguish, and in his developing madness, he thinks that I am giving him advice about how to deal with it when he sees me on television.

The invitation to take part came out of the blue, and I assumed Jimmy McGovern, who I first met at a MIND charity event we were both supporting, was aware that when I went mad in the 1980s, and ended up in hospital, I was convinced Des Lynam was reading the football updates to me on Grandstand, in code, and that if I cracked the code, I would be allowed out. I spent hours doing anagrams of East Fife 3 Albion Rovers 2 and the like, to the seeming consternation of the nurses. Then I got a phone call from an old pal, Chris Boffey. We chatted away and after a while he mentioned that he would be watching Taggart on TV later.

And then he added, very slowly, ‘you know the one … About the Scottish detective with a smile carved out of granite’.

At the time, I was in a Scottish hospital, having been sent there by two Scottish detectives not dissimilar to Taggart who had arrested me for my own safety because I was behaving oddly.

‘Thanks Chris,’ I said, quietly replacing the receiver, then cursing myself on realising that Des was a decoy, a waste of my time, and my friend was advising me that the real route to escape was via Taggart. I had to study the smile, develop it, practice it, deliver it to the doctors and nurses, and I would be free.

The next few hours seemed to drag on forever but eventually Taggart was on. He didn’t smile much, but when he did, it was indeed a tough man’s smile. I saw it three, maybe four times, went to the bathroom to practice in front of the mirror, back to bed, called for the nurse, told her I had cracked the code, did the smile …. And then…

‘Eh, I wonder if we might not need to up yer dose, darling,’ she said, another plan reduced to nothingness.

So when I arrived on set – how exciting does that sound? – and met Jimmy in the (equally exciting) location catering bus, I said I guess you asked me to do this because of Des Lynam and Taggart – at which point he looked at me a bit like the Paisley nurse had done in 1986.

Lunch over, into make-up, final swot on my lines, then lights, camera, action. As a student of power, I found it fascinating to see where the power lay on a film set – my assessment was director, cameraman, producer, writer, actor – in that order. They knew what they wanted, they knew they were not dealing with a professional, but they were determined I would be the best I could be. I had a 12 line monologue, delivered direct to camera. I did a little crib note of key words which I stuck to the bottom of the camera lens. The cameraman reacted as though I was not the first person he had worked with to have done likewise. Somewhere between six and ten takes later, we were done.

Fair to say I have a small part, but a big role in the plot, which carries on without my face next week. I enjoyed it, tiny though it was, and the final product – the film as a whole – is really powerful, and next week’s in many ways even more so. So tune in, not for my cameo, but for top quality TV drama the likes of which Elizabeth Murdoch was saying Britain does best in her thoughtful and interesting Mactaggart Lecture.

So anyway, enough of all that excitement … Here’s more. As a result of chatting to Jimmy, once he had recovered from my Des-Taggart psychotic recollections, we got chatting about mental illness and he made the extraordinary confession that he hadn’t yet read my first novel, All In The Mind, despite Stephen Fry’s observation that it was as brilliant a study of the human mind as he had read… Jimmy was about to go to Vietnam, and he said he would take it with him, and read it there… and I thought blahdiblah, another bloody luvvie, he’s got what he wants out of me, and I will never hear from him again.

Me of little faith. A few weeks later, he emailed to say he loved it. Then Sita and Roxy emailed to say Jimmy never enthused like he had about this, so they read it too, and the next thing they were sitting at my kitchen table, buying the rights for a TV adaptation.

So that’s why I am excited. I know lots of books get bought and films never get made. But Jimmy McGovern is Jimmy McGovern, and if you watch ACCUSED, you will know that he, Sita and Roxy just get this stuff about what goes on inside troubled minds.

All in the Mind did well for a first novel, and I hope has played its own part in the campaign to get mental illness more out into the open. But a Jimmy McGovern adaptation will do a hell of a lot more, so I am not just excited but grateful.

I took a while before deciding to say yes when he first asked me to play myself. But at the time I was working on The Happy Depressive, and reading about the happiness’ experts view of happiness ingredients. One was ‘keep trying things you have never done before.’

So I said yes, and one thing has led to another, and I’ve got a feeling it’s going to be good – however badly my acting debut goes down with the critics who don’t blink.