It’s, ah, Hugh Grant here. Here at the doorstep, in fact, just doing my bit

Imagine it. One morning, your doorbell rings. You shuffle downstairs, expecting to see the postman with a Christmas parcel. But it isn’t the postman. Nor is it the gas man, a Jehovah’s witness or a dubious looking man purporting to sell domestic cleaning products.

No. It’s Hugh Grant. “Ah! Er. Yes. Good, er, morning, madam. My name is, ah, Hugh, and I’m here with … well, anyway, the very fine Liberal Democrat candidate for … your area.

“And, ah, we were rather hoping – if it isn’t too much trouble – that, not to put too fine a point on it, you would accept this rather lovely, well, item of campaign literature, I suppose you could call it – do take a look, if you happen to get a moment, it contains some terribly, um, informative bar charts …” The scenario sounds farfetched. But it may be playing out at this very moment, somewhere in the better-heeled parts of London – because the star of Love Actually is spending the election as a roving advocate for tactical voting.

Some days he helps out a Lib Dem candidate; other days, a Labour candidate.

Whichever one, in a given constituency, is considered most likely to defeat the Tory. Because Mr Grant has vowed to do what he calls his “modest bit” to help stop Brexit. Yesterday afternoon, in a leafy square near Parliament, he was invited by Chuka Umunna (ex-labour, now a Lib Dem) to give a pep talk to party activists. Siobhan Benita, Lib Dem candidate for the London mayoralty, introduced Mr Grant by promising that she would do her best “not to swoon”.

Mr Grant – silver-haired and approaching 60 – gave a small, and perhaps slightly long-suffering, smile.

His speech was short, but fascinating to watch, mainly because it was so … him. Or at least, how you imagine him to be. It felt as if we were watching a clip of Hugh Grant playing Hugh Grant in a biopic of Hugh Grant. The murmuring self-deprecation, the brief rueful grin, the air of mildly pained forbearance.

“I don’t want to sound dramatic,” he said. “Although you could argue that that’s my job …” (Pause for activist laughter.) “But I really think we’re facing a national emergency …

“What’s left of the Conservative Party, now they’ve expelled anyone who is responsible or decent or sane, is not something I can contemplate as the government of the country I love…” Activists gazed at him soupily. He took a couple of questions from the press. Yes, it had “crossed my mind” to stand for election himself, but he suspected he was “too old and pleased with myself ” to obey party whips.

Had he ever been canvassing before? No, but he did used to be a door-to-door salesman, selling fire extinguishers and coat hanger covers. “I was very good … I might go back to that …”

Wise words. Sadly, he may find more people want coat-hanger covers than Lib Dem leaflets.