Upstairs in his kitchen, he offers me coffee brewed in Byron's friend Trelawney's particular way. Pull the coffee-pot off the light just before it boils, stir, put it back again (having extinguished the light), and let it foam up delicately. I am examining prints of famous portraits of Cole-ridge on his sitting-room wall, and examining the books in the book- cases: the collected journals of Byron, published by John Murray, who published one small volume of Coleridge's poetry on Lord Byron's recommendation, but soon dropped him like a stone. Holmes walks in with the cups and laughs: "Looking for a story?" What else?
Holmes discovered a passion for biography in the 1960s, pursuing the ghost of Robert Louis Stevenson through the villages of the Cevennes. A few years later he was on the track of Shelley, going everywhere that Shelley went, amassing the materials for a life that became his first major excursion into literary biography.
But for the past 15 years (with interruptions) he has been co-habiting with Samuel Taylor Coleridge. This month sees the publication of Coleridge: Darker Reflections (HarperCollins pounds 19.99), the second volume of his massive 1,000-page biography of one of England's greatest and most extravagantly flawed geniuses.
Hilary Spurling once described Richard Holmes as a kind of amalgam of the Scarlet Pimpernel and his namesake, Sherlock. Today, this genial, balding man in his early fifties looks like a prosperous professional temporarily resting after years of unstinting labour at congenial work. I ask him why anyone would want to be a biographer in the first place. Isn't it an act of self-denial?
In part, he agrees. Yes, he replies, it ought to be an ideal transparency, a window on to a soul. But there's more to it, and this has to do with the fact that it has become so alive as a literary form. Biography, he argues, has stepped in to fill in a gap created by the collapse of the traditional novel. Now biography is the storytelling form and, like a novel, it requires shaping, pacing, rhythm - quite apart from all the research.
One of the astonishing aspects of the life of Coleridge is the number of years Holmes has devoted to it. Indeed, in Footsteps, his own account of his early life as a biographer, he wrote of his subjects in terms that recall Christ and the disciples: "If you are not in love with them, you will not follow them."
Could Holmes conceive of the possibility of falling out of love with the subject of a biography? No, this hadn't happened to him. The more maddening he found Coleridge, the more he grew to like him. But the relationship had been changing all the time. "The point is that you are not the Counsel for the Defence. You see your subjects broadly and deeply and that may include great criticisms."
But Holmes would not write a life of someone who is alive. There has to be that necessary distance - three generations or so, in his case. And an essential part of the task is to resurrect the entire period.
"Biographers of the living," on the other hand, "are almost a contradiction in terms. If you're writing what is practically contemporary history, trespassing on what is in effect journalism, the interview, it becomes an entirely different form."
Certain lives lie beyond the reach of the best biographer. Holmes once wrote a 400-page life of the 19th-century French poet Gerard de Nerval. His publisher would have been happy to publish it, but Holmes withdrew it. What happened?
In order to write a comprehensive and convincing biography, you have to establish consistency between the inner and the outer man. If there is no consistency, the project collapses. In spite of the fact that Coleridge was a man of immense complications, his life - and his own thinking about his life - are immensely well documented. Cumulatively, his writings add up to an astonishingly full portrait of a mind.
There was no such wealth of evidence in the case of Nerval. He wrote an account of his own childhood, but it was a very artful document, which could neither be properly verified nor improved. Then there was the madness which gradually overtook Nerval. Holmes reluctantly concluded that he would be doing the memory of the man a great injustice by telling his story.
So he has concentrated the greater part of his energies on the lives of two English Romantic poets. Did he think poetry a greater art than fiction or biography? Holmes looks uncomfortable with this talk of hierarchies. But he hazards an answer: "If there is a hierarchy, I think that biography, which is my passion, comes quite low in it... Poetry? Well, there is something about the language of poetry which makes it the cutting-edge of all written art forms." Yet he looks troubled, as if some part of him might be at odds with his own conscience.
But he cheered up when I asked him why Romanticism had been such an abiding preoccupation. Could it be that he was a child of the Sixties? Yes, there was certainly a kind of "harmonic" between those two generations of Romantics. But it was also something to do with the way in which English had altered all of a sudden, some time between 1750 and 1790. He could sense the resonance of that period. "It's such a wonderful period. Those people are so exciting to deal with. They're full of ideas and hopes and passions... I just love the fizz and excitement of it, and the hope in it - that is a great theme in Coleridge, the nature of hope. The more I think of it, the more precious a commodity it seems, Hope with a capital H."
And the English sun, curmudgeonly as ever, still refuses to endorse such a powerful display of heartfelt feelings.
Richard Holmes will discuss `Coleridge and Revolution' at 1pm today, in Cheltenham Town Hall