Later this year, the actor and explorer Brian Blessed will scour the remoter regions of Russia, China, Sumatra, and Bhutan in search of the yeti. You get the impression, though, that if he ever came face to face with one, it would be Big Foot scurrying for cover, intimidated by Blessed's sheer life-force. Larger-than-life doesn't even begin to describe him. "I'm a law unto myself," he roars. "I can't be restrained." You can say that again.

Passion pours out from every pore. But what is it that gives this man of 61 the energy of a 16-year-old? "Love of life," he replies, simply. "I find I spend all my time saying thank you for being alive. Getting up every morning is a miracle. Life is an amazing gift. Despite what people say about me, you can't actually be larger-than-life - because life itself is so large. I have a big frame and a big voice, but they just serve me to express my love of life."

The latest project he is attacking with the zest of Ronaldo taking on defenders is the direction of a production of Tennessee Williams's The Glass Menagerie at the Battersea Arts Centre. Starring his wife, Hildegard Neil, the show marks Blessed's directorial debut in the theatre.

"I'm not being paid a penny for this job, but I love encouraging young people," Blessed explains. "I was brought up a coalminer's son in the same Yorkshire village as Patrick Stewart. At the time, it was inconceivable that we could be actors, but everyone there helped us with scholarships. When the company putting on The Glass Menagerie came to me and said, `Would you look at it?', I said, `Yes'. I rehearsed with them for three days before having to fly off on an expedition. I got all the way to Patagonia and said, `I've got to go back and help these people. Three days is not enough'."

He came up with with a radical reinterpretation of the play. "In the past, I've always been bored shitless by productions of The Glass Menagerie. They're always gloomy, and that's not what it's about. This is a play about hopes and dreams. It is not depressing. Williams said, `I love magic,' and there are more special effects in this than in Star Wars. I've put in the music from the 1920s' Superman and `Ave Maria'. The narrator's first line is, `This play is not real', so I have Williams as the narrator walking around giving lighting and music cues."

As if he didn't already have enough on his plate, Blessed this week is flying off to a mountain range in deepest Venezuela, 80 per cent of which has never been charted by humans before. It was the inspiration for Arthur Conan Doyle's Lost World.

Since the age of 53, when Blessed first attempted to scale Everest, he has developed a second career as an intrepid explorer. "Adventure is the key to the future," he enthuses. "We're frightened of silence. We all need 40 days and 40 nights in the wilderness like Jesus Christ. When you go into the wilderness, you realise what an aggressive animal man is. You have to be careful when you go near gorillas because you stink of thousands of years of war.

"The greatest danger in life is not taking adventure. If the RAF say they want to parachute me down a mountain, I leap out of my seat with excitement. Exploring makes me feel free. The idea that 40 is middle-aged is crap. It's not how old you are, it's how you're old. I meet 80-year- olds on Everest.

"In the mountains, you get a sense of limitlessness. Here we're always bending the laws - in our cars, for instance - but there, if you break the law, you die. You have to listen to the music of the spheres there. We all have our own Everest - it could be a garden or horse-riding - and we must go for it. We mustn't let the bastards grind us down."

Blessed has brought the same joie de vivre to his acting, in such notable works as Z Cars, Cats, I, Claudius, Flash Gordon, and Kenneth Branagh's Henry V and Hamlet. His most recent success was as the raging Squire Western in the BBC's adaptation of Tom Jones.

He was born for the part and was desperate to play it. "I said to the director, `If you see any other actors, I'll tear their heads off'," he laughs. "Hugh Griffith made a marvellous job of it in Tony Richardson's film, but I made Western more frightening. When he hates, he hates. It pulsates in his veins like yeast. The part is so extravagant, yet it requires subtlety to make him real. The director pointed out what a dangerous man he is. You never quite know what he's going to do. He said to me, `Western is a Force 10 gale'."

We're likely to see Blessed next giving it some serious Force 10 in George Lucas's continuation of the Star Wars saga, in which he plays the king of the water-planet where the action is set. "As one big star said to me the other day, `I'd be a bloody grain of sand in Star Wars'. It's Boys' Own stuff. You come away from the films feeling purified."

Sadly, however, we won't be treated to Blessed in Earth Scum, a new US sitcom with a passing resemblance to Third Rock from the Sun. "I've just come back from Hollywood where they offered me the sky to do the series. But you have to sign up for six years, and I can't face being in LA. Also, if I did the bloody series, I wouldn't be able to go to Everest. They'd say, `You can't go on your expeditions, you'll get malaria'."

Certain B words attach themselves to Blessed like Italian man-to-man markers: bombastic, booming, bearded, belligerent. There are no doubt elements of them in him, but they are all mere by-products of his most striking quality: he is a man Blessed with boundless enthusiasm.

This is what makes the very idea of retirement alien to him. "Pension? Retirement? Bollocks to all that. I don't want all that crap. You don't get retirement from life - just keep your arse moving. I'll go down with all guns blazing."

`The Glass Menagerie' is at the Battersea Arts Centre, SW11 (0171-223 2223) from 30 June to 19 July