Boris Johnson is working the crowd in front of an Ealing hairdresser's shop, apparently unaware that the sign above his trademark tousle reads Sheer Hair. I take a snap on my mobile phone and post it on Twitter.
Since playing a cabinet minister in the BBC2 series The Thick of It, I've been asked to do many things not commonly within an actor's remit: appearing on Question Time, a part in a Labour Party political broadcast (Have they not seen how hopeless my character is?) and now following Boris as he tours Ealing in west London, drumming up support for the Conservative candidate, Angie Bray.
The Tories have kept London's Mayor out of the spotlight for much of the campaign, possibly to deprive the electorate of the opportunity to get a winning hand in a game of Bullingdon rummy, but more probably because of his wilful refusal to speak like a party apparatchik.
Boris, whose second anniversary as the most powerful Conservative in public office falls today, is referred to as "gaffe-prone". But aside from the odd moment of slapstick (who can forget him falling in the canal he was helping to clean?) I suspect most Borisisms are more canny than careless. Inside that Bertie Wooster exterior is a Jeeves-sized intellect.
When the Mayor publicly berated David Cameron for not making his flagship idea for a national citizen service compulsory, I don't suppose he did it by accident. So it looked as if he'd been locked in an attic, like the first Mrs Rochester, but been allowed out for such light buffoonery duties as his speech in praise of England, custard and St George.
Now he's in west London, glad-handing all comers. He looks baffled at my presence in the entourage of political journalists and party activists. "You're an actress," he says, peering at me through narrowed eyes. I tell him I'm in The Thick of It, and he announces to the assembled press, surprisingly, that my character is his political role model. "Inspiring people out of poverty" he quotes from one of the episodes. "Marvellous." The episode to which he refers concerns a nonsensical social affairs initiative called The Fourth Sector. I tell Boris many people have drawn comparisons between its vague, do-gooder lack of definition and Cameron's Big Society agenda. He laughs, and claps me on the arm in a clubbable fashion.
He seems happy for me to trot alongside eavesdropping, although when he slips into a shifty-sounding conversation with a stall-holder about the best kind of tobacco for a shisha pipe, and I tell him I'm going to put it in the article, he squints at me again and says: "I'm worried about your article."
You may not share his views, be a fan of his mayoral achievements or his tendency to throw political correctness to the four winds if he thinks it will improve his rhetoric (remember the furore over his use of the word "piccaninny"?) but he's got something.
Sometimes, on TV, he exhibits a slightly superior smirk, as if he can't be bothered to take anything seriously. But in person he slips seamlessly from snatched Oxbridge banter with one man – "Were you at Trinity?" "No, but I had a girlfriend who was ..." – to a carefully worded answer about immigration. When a passer-by accosts him about parking laws in Kensington, Boris asks: "May I ask where you're from?" "I'm Italian," the man replies. "Buongiorno," the Mayor beams. "Now let me introduce you to my colleague. He knows about parcheggio in Kensington."
An employee of a phone shop emerges with a present for the Mayor, a replacement for his "knackered Nokia". Boris explains that he can't accept the gift, so the man suggests he might like to buy the phone from him instead. Boris seems delighted by the man's "entrepreneurial spirit".
After a fleeting visit to a café where the manager has, implausibly, adorned his walls with pictures of James Dean, Al Pacino and Boris, he finishes his walkabout and I mention that one bookie has him at 3-1 to be the next Tory leader. He claims not to know this.
I can't see it happening, but if it ever does, it will be because of his cavalier disregard for saying what politicians are supposed to.