Hugh Grant lifts the mood a little at a secret Lib Dem gathering

They arrived in dribs and drabs – like sleeper agents converging on a dead letter drop – from all corners of a small public garden in central London. A few spoke to one another, the rest rather kept their distance until their handlers arrived with yellow clipboards. This could have been the most clandestine meeting of Lib Dems Anonymous.

“Hi. I’m Jo. I’m a Lib Dem.”

“Hi Jo. Would you like to share something with us?”

After several awkward silences, there was a flurry of excitement as a man with film star good looks appeared. Closely followed by the actor, Hugh Grant. If Chuka Umunna fails in his bid to win the Cities of London and Westminster seat, formerly held by Mark “grab a female protester by the neck” Field, then he has a lucrative career ahead of him as a catalogue model. Something that at the moment appears all too possible as Umunna is currently polling eight points behind the new Tory candidate, the former leader of Westminster council. Clearly the local residents have warmed to the prospect of the woman who has done most to cut their local public services.

This hasn’t been the best of campaigns for the Lib Dems. They started off bullishly insisting they could win more than 100 seats. But their “revoke article 50” declaration, combined with their insistence that Jo Swinson would be the next prime minister, went down spectacularly badly with the public and they are now down to damage limitation.

Which is where Hugh comes in. Taking time out from playing a prime minister the country happened to like in Love Actually – not to mention a Lib Dem leader, Jeremy Thorpe, who was lucky not to get sent down in A Very English Scandal – the actor has downgraded himself to political activist.

The introductions were made by the Lib Dem mayoral candidate, Siobhan Benita, who said she would do her best not to swoon over the presence of a Hollywood star.

Hugh raised an eyebrow and looked as if he’d rather be elsewhere. As if he was fed up with being objectified for his body. How come no one fancied him for his mind? Hell, anyone would have been outwitted by Paddington Bear. There was no disgrace in that. The burden of having come close to being a national treasure weighs heavily on him. He is not an actor who outwardly seems to enjoy his success.

But Grant is nothing if not professional and right on cue he delivered his lines. He didn’t want to be dramatic – pause – though obviously that was his job, but the country was facing a national emergency. The Conservatives had been hijacked by the far right. So he was stepping forward to do what he could by campaigning for candidates in marginal seats where there was a chance of stopping the Tories from winning. He wasn’t particularly wild about the Lib Dems – though he was fond of “Chooka” – but needs must to get a hung parliament and the chance of a second referendum.

Umunna wasn’t at all bothered that Hugh would be off campaigning for Labour on Wednesday. Rather he was just grateful for his support for even a couple of hours on a bleak December afternoon. Umunna never looks rattled by anything, but he knows he and the Lib Dems are now in the last chance saloon. The situation is desperate.

Twice he admitted he was down to trying to snatch victory from the jaws of defeat and that his only hope was a massive surge in tactical voting. There is a new pragmatism to Umunna. First we take Westminster, then we take Boden.

There followed a somewhat awkward huddle. Grant has no great fondness for the media – since 2011 he has been one of the leading campaigners for Hacked Off – and he remains well-guarded in any interactions with journalists. So this one was kept short and sweet. No small talk. Nothing too personal. Nothing that could be construed as a sign of weakness or used against him.

Yes, he had considered a career in politics but concluded he was too old and too pleased with himself to follow a party line. Yes, he would be prepared to pay more tax. If not always cheerfully. Unlike some newspaper owners, he had never been a non-dom.

The closest we got to ersatz romcom intimacy was the admission that he had once been a door-to-door fire extinguisher salesman. Was he any good? “I was actually,” he smiled. “I also sold coat hanger covers.” Highly flammable ones, presumably, so he could include them in a two-for-one offer with the fire extinguishers.

And that was it. End of. Grant and Umunna were off to go canvassing and I wasn’t welcome to join them. Voters might get too much of a surprise if there were journalists present. Though obviously they wouldn’t bat an eyelid to find a film and TV star on their doorstep.

It was all rather low-key. Though it had been that kind of a day. After a weekend spent trying to make political capital out of the London Bridge terror attack, a dishevelled Boris Johnson and an unusually well-groomed Jeremy Corbyn had restricted their public appearances to attending a vigil for the victims. The lull before the storm. Later that night Donald Trump would arrive for the Nato conference. Then almost anything could happen.

John Crace’s new book, Decline and Fail: Read in Case of Political Apocalypse, is published by Guardian Faber. To order a copy go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £15, online orders only. Phone orders min. p&p of £1.99.