Despite enjoying filming the new Richard Curtis movie in Cornwall, Bill Nighy feels more at home at a London café. But wouldn’t he be suave and relaxed anywhere?

Sitting with Bill Nighy for a few hours on the pavement outside an Italian deli in Notting Hill is an extraordinary experience. First, there are his carefully chosen drinks crowded onto the tiny table: a double espresso with hot water on the side, a bottle of fizzy water, a cold can of San Pellegrino Aranciata Amara, two tall glasses with ice and a slice of lime. When, later, some of the drinks are finished, he is suddenly irritated by the chaos and politely announces he can’t settle until he has moved the debris onto another table.

Then there’s the steady stream of traffic heading down the hill towards Shepherd’s Bush. Every now and again, an excited teenager will squeal Nighy’s name out of a car window. He will slowly and slightly regally raise a hand. Occasionally, a breathless girl will be nudged towards our table. One says, ‘My friend just referred to you as a legend.

I thought you might like to know.’ He thanks her and happily signs an autograph with a glitttery, feathered pen. After being baffled for a good half-hour, I realise they’ve all seen him in Harry Potter and the Deathly Hallows as Minister Rufus Scrimgeour.

At one point, I go to the bathroom and discover when transcribing, that, in my absence, a woman has approached and tentatively asked him who he is. Quite without ego, he says to her, ‘Well, I’m an actor. My name is Bill Nighy. You might know me from Love Actually, in which I play an old rocker. I’ve just got one of those faces.’

Nighy, a youthful 63, is one our finest actors. Starting off at the Everyman in Liverpool, he has worked with most of our best writers, including David Hare, Tom Stoppard and Harold Pinter. Despite not being at all posh by birth – he was born in Caterham, Surrey, to a psychiatric-nurse mother and mechanic father – he has something of the English stiff upper lip that is, thank goodness, diluted by an innate playfulness.

He’s exceptionally good company. He has a wonderfully dry sense of humour. Mostly, it has to be said, when it comes to clothes. Today, he is dressed down in a beautiful light blue shirt, dark blue jacket and jeans that look as if they might have been dry-cleaned. He always says he will never do Shakespeare because of ‘the stupid trousers’, even though he was fantastic as Edgar in David Hare’s King Lear in 1986. His performance even inspired a 14-year-old Rachel Weisz to act simply because she had never thought Shakespeare could be so rock’n’roll.

He talks about an upcoming role in which he will play a Welsh miner during the strike of 1984-85. The film’s script is written by Stephen Beresford (whose play The Last of the Haussmans was a hit at the National last year) and is also set to star Imelda Staunton, Paddy Considine and Dominic West. It’s a great story, about a group of gay men and one lesbian who raise money for the miners. But what will the king of sartorial elegance wear? ‘Well, I once played a farmer. I say to people, “Laugh if you want, but I’m playing a Welsh miner.”’

Nighy likes to say, in his languorous voice, that he will only ever wear ‘a decent lounge suit’, preferably blue, both on and off screen. ‘It’s a riff. I make myself laugh, if nobody else. If you’re to appear in public, you want to look your best. I can operate better in a lounge suit. And I like saying the word “lounge”. It’s such a stupid word to say in this day and age.’

Yes, but Welsh miners didn’t wear lounge suits, especially not when on strike. He raises an eyebrow and laughs. ‘Look, I did a snowboarding movie once. They did find me the only navy blue salopettes in the whole skiing community. I was very, very grateful. They didn’t even ask; they just knew. At least I didn’t have to wear electric orange.’

Nighy is always a treat to watch on screen – or just to hear, as his disembodied voice in Edgar Wright’s film The World’s End recently reminded us – that it’s hard to believe he ever suffered serious nerves. ‘I found it extremely difficult being an actor when I was younger. It’s amazing that I persisted.

I have no idea why I did.’ What was he like as a younger man, once he’d given up on the idea of running away from Caterham to be the next Ernest Hemingway? ‘I was an average mess in terms of what went on in my head. I was uptight, as we used to say in the old days, but trying to appear cool.’

After training at the Guildford School of Acting & Dance, he used to worry about being found out as a fake. ‘When I was young, it was chronic. I used to visualise it all in great detail. A director tapping me on the shoulder and saying, “Bill, it’s not working out. We’re going to have to let you go. We just don’t have the time.” That era has passed. I am, to some degree, reassured by my experience.’

He must also be reassured by two of our most successful directors, David Hare and Richard Curtis, not just using him time and again, but also writing parts with him in mind. It was David Hare who first saw Nighy’s potential to play a romantic lead in his 1980 television play Dreams of Leaving. They have been good friends ever since and this summer filmed two follow-ups to the terrific spy drama Page Eight – Turks & Caicos and Salting the Battlefield – to be screened on the BBC next spring.

Nighy says he admires Hare ‘as much as anyone in the world’. He then recalls appearing in one of Hare’s plays, The Vertical Hour, in New York in 2006. ‘Every single opening night of my theatrical career, I’ve waited in the wings saying to myself, “This will never, ever be allowed to happen again.” But the relief afterwards is tremendous. After the second night of The Vertical Hour, I was being driven back to my apartment in a big black SUV and I asked Andrew, my driver, to pull over so I could buy some M&Ms…’

He pours some San Pellegrino; he hasn’t had an alcoholic drink for years. ‘…I used to have a serious M&M problem. I loved getting them in every colour in America. Anyway, it dawned on me: we’d opened. I had my M&Ms and Barry White’s ‘Never, Never Gonna Give Ya Up’ was on the radio. I said, “Turn that fucker up! Let’s go to Brooklyn for dessert!” Andrew put the wheel between his knees and we were both waving our arms about. It was bliss. Ecstasy. Absolutely uncomplicatedly OK.’

On a roll now, he talks about acting with Christopher Walken in Turks & Caicos. ‘He was hilarious and marvellous. So funny it almost hurt. He’s my American acting hero.’ We sit for a moment, silently appreciating Walken.

If Hare made Nighy a romantic lead, then Curtis pushed his fees up. After Love Actually, he was suddenly properly paid. In Curtis’s new film, About Time, he time-travels in a fantastic house in Cornwall. That must have been fun? He pulls a face. ‘I had all kinds of crises.

I didn’t sleep. But it was very, very nice being in Cornwall. I was overwhelmingly moved by it. I used to go and get a pasty at the end of the day and sit on the beach. I really dug it.’

Would he ever leave London? ‘I always think about it. You get to my age and you’re supposed to buy a dog, aren’t you? I don’t suppose I’ll ever leave London, but I do want a dog.’ Not a cute puppy, though; he walks pretty much everywhere in London and would never get anywhere.

We talk about his beloved Crystal Palace and politics – for the past five or six years, he’s been visiting developing countries and campaigning with Oxfam at G8 and G20 summits and is furious that extreme poverty isn’t further up our government’s agenda. ‘Richard Curtis is remarkable. He quietly gets on with raising enormous amounts of money. He took over American Idol for one episode and made $76m in donations in an hour.’

Nighy himself is pretty remarkable. Polite, old-fashioned and with no hint of actorly pomposity, his very presence in a film or play is guaranteed to lift it to another level. I leave him sitting in the late-afternoon sun, sipping on fizzy water and waving patiently every now and again at his fans.