Sir Peter Blake: It's not rock'n'roll but I like it, says Sir Peter, faithful devotee of the House of Windsor

Peter Blake almost managed to keep his knighthood secret over the five long weeks since he received the letter from Downing Street asking him if he would accept the honour. But at the wedding of his fellow knight and old friend Sir Paul McCartney, he finally blurted it out. "We hadn't even told Rose, our 15-year-old daughter," says Blake, in between the many congratulating phone calls that punctuate our interview.

"We managed it until Tuesday night when we went to Paul McCartney's wedding. Naturally, I got rather drunk and I told Paul. He was very excited and he gave me a big hug. I told George Martin too, but as they're both sirs anyway they've been through the same process and I assumed they wouldn't tell anybody."

So now arise, Sir Peter Blake, along with Sir Mick Jagger and Sir Jonathan Miller. The rebels of the 1960s have finally accepted the accolades that signify they are a part of the establishment they once shocked. Except this does not represent any kind of volte-face for Blake. He may be for ever associated with the decade of Swinging London after designing the cover of Sergeant Pepper's Lonely Hearts Club Band, but this genial, slightly plump Father Christmas of a man was never the type to return an MBE, as the Beatles did. Anyone who expects him to conform to the stereotype of a counter-culture artist railing against the institutional hierarchies is in for a surprise. He turns out to be an ardent, sentimental monarchist.

"My grandmother was an absolute royalist; she came to London for every occasion. When I was a kid, I went to the Victory Parade after the Second World War, and I went to the Queen's wedding. I couldn't go to the Jubilee, but that's about the only one I've missed. I went to Princess Margaret's wedding to Tony Snowdon, and we went to Charles and Diana's wedding. I've always been there on the street with my flag waving. I think if I was cynical about royalty it would be less of a pleasure."

Blake is touchingly pleased by the honour, as are the friends who have set his Mae West lips phone ringing all morning. He's happy with the timing, too. "About 10 years ago, two people separately hinted to me that I might be getting this letter, and it didn't come," he says. "I thought that was it, so it really was a great surprise. I'm 70 next week, which I think is about the right age to get it. Ten years ago would have been too soon and five years' time might be too late." He's also delighted to receive the honour in such a significant year for the monarchy. "I started as an artist almost exactly 50 years ago. In 1953, I went to the Royal College as a student. So what's particularly nice about it happening in Jubilee year is that my career exactly parallels the Queen's reign."

Whether Mick Jagger, whom Blake has known since childhood, would be quite so loyal is questionable. But the artist has no doubt the Rolling Stone does deserve his knighthood, and has no time for the view that Jagger's rackety lifestyle makes him an unsuitable recipient of the honour.

"When we were kids, we lived about 50 yards apart. I didn't really know him because he was 10 years younger than me, but he was a friend of my brother's; they went to Dartford Grammar School together. Since then we've met over the years, last time at the Q awards when he made a point of coming over and giving me a big rock'n'roll hug.

"I think whether he's a tax exile or not is irrelevant. He's been given it for services to music and he's served music well over the years. It would be nice to have a Sir Keith too, but I don't expect that's going to happen."

The knighthood is not the only early 70th birthday present to come Blake's way. "A lot of nice things have happened," he says. "I'm going to be Professor of Drawing at the Royal Academy schools for the next two years, which is kind of an honorary thing. I don't particularly have to go and teach, just encourage the art of drawing." And the next Harry Potter film will see Blake take a cameo role. "A friend of mine is the first assistant director on the film. Justin de Villeneuve, who's another friend, is going to be a wizard in the one they're making now, and he said do I want to be a wizard too. So we went down to the studio – looking like wizards anyway – and got costumed up, and next week we're going to be filming three days. Quite suddenly as I approach 70 it's all gone like fireworks, it's all exciting and wonderful."

There are those who spurn honours as the baubles bestowed by anachronistic monarchies. But it would take a stony heart to begrudge Blake the genuine and humble pleasure this award has brought him. Arise, Sir Peter, as trusty and faithful a knight as any who have served the House of Windsor – or appeared in a Harry Potter film.