On 27 December, after the big movie at 10.50pm on BBC1, my film Sorry About Last Night is being transmitted. This is a hilarious romantic comedy starring myself and the wonderful Siobhan Redmond, and I have been travelling round the country publicising it on local TV and radio. Mostly I travel on these excursions by train because travelling first class on the train is, or at least used to be, a lot more relaxing than travelling by car. Even five years ago first class on the InterCity used to have the contemplative calm of the British Museum Reading Room - occasionally, servants would glide in offering coffee and mints, but apart from that the studious atmosphere meant you could read or catch up on some writing, but not no mo' homeboy! As I sit here on the four o'clock going up to Manchester, there is an appalling cacophony going on around me. There are two men muttering business stuff into little micro tape recorders, there is the clack-clack of keyboards of three laptop computers and, of course, worst of all, there is the constant chirrup of mobile phones ringing. In order to blot out all these distracting noises I've been forced to take up the jazz trombone, on which I practise my scales as we whizz through the countryside. If I don't have my trombone with me and I don't want to be left out in the noise-making stakes, then I just shout into an old biscuit tin at my imaginary friend Geoffrey. "Hello, Geoffrey," I yell at the top of my voice, "It's me, Alexei. I just wanted to tell you we've just passed through Nuneaton - should be in Stafford in a bit. Yeah, I'm going to ... hello? ... hello? ... sorry, we got cut off for a minute there, Geoff. We went into a tunnel ... hello? ... hello? You still there? Hello?"

Mind you, an even worse phenomenon than mere noise pollution occurred to some friends of mine recently. They travelled first class to Manchester and back to see United play Chelsea at Old Trafford and both ways they had the misfortune to be seated next to what they said was the most appalling Eighties-style, upper-class yuppie, who brayed all the way up on his mobile phone about stocks and shares and skiing holidays and all the way back on the return trip he shouted into his phone various racist remarks about some of the black players.

I've been unable to forget about this incident since I heard the story - and I've never ever regretted not being somewhere more than I've regretted not being there. And I can tell you I've missed out on some big stuff in my time: I turned down an invite to an epoch-making early Sex Pistols gig on the grounds that I was going to stay in and wash my hair, and once, and I swear this is true, I was making a film in the South of France and the female lead (the Flashdance star Jennifer Beales, one of the most beautiful women in the world) invited me to dine with her at Paul Bocuse's restaurant just outside Lyon - probably the best restaurant in the entire world and I turned her down! Because I was fed up with French food and I wanted to go home and at the exact time when I could have been dining on wild strawberries with this gorgeous intelligent woman I was eating a Ginsters Cornish Pasty on Dover station, so don't tell me about missed opportunities.

But I wish more than anything that I'd been on that train with that horrible bloke because, after all, how often do you see a yuppie these days, much less beat one up? And the great thing would be that while you were smacking this bastard you'd be advancing the cause of anti-racism at the same time.

However, I wasn't there. We get so few chances to test ourselves these days - it's got to be a once-in-a-lifetime opportunity to do the right thing, to make a principled stand, and I missed it. So now I fantasise endlessly about what I'd do in that situation - whether I'd just quietly lean over and say: "Mate, how about keeping your filthy racist remarks to yourself?" and then when he inevitably gave me some lip I'd pop him one in the mouth, smack, just like that. Yes, I'm almost definitely certain that if I was in that situation I'd probably absolutely definitely do what was the right thing, almost no doubt about it. But I wasn't there, so I dream on. I think that maybe I'd just ask to have a look at his phone, then, when he proudly showed it to me, I'd stamp on it and smash it into a thousand pieces and then I'd fight with him - even if he was much bigger than me. Also in some of my fantasies about this evil git I'm wearing a strapless black cocktail frock and high heels - but we won't go into that.