Thomas Sutcliffe: An American Treasure in Britain

"The house has its own will to survive", says Marcia Balisciano, climbing a narrow wooden staircase so skewed and exhausted that it looks as if it is only just clinging on to life. The house is 36 Craven Street, a Georgian terrace just to the west of Charing Cross Station, and Marcia is the Director of the foundation dedicated to restoring it. Fortunately, the impression of imminent collapse is misleading. The door frames may be canted parallelograms, the ceilings may sag like pregnant mares and the original floors roll like a heavy Atlantic swell, but the building is now stable, thanks to £814,000 pounds of structural work ­ funded in part by English Heritage, the Getty Foundation and the Heritage Lottery Fund.

As you pick your way through the house, past panelling still marked up from its jigsaw reconstruction and over holes in the broad 18th-century floorboards ­ you occasionally catch glimpses of the steel ties and I-beams which ensure that the building's long slump into dereliction has now been frozen. Phase II of the project, for which they are now actively raising another £1.66m, will involve restoring the interiors to their original appearance.

"Former glories" would be going too far here, because charming as it is, there is nothing about the building itself which could account for such lavish rehabilitation. It is, concedes Balisciano, "a workaday middle-class house", one of a number of spec-built homes that huddled up against Northumberland House, which used to occupy the space where the station now stands.

But for 16 years 36 Craven Street was the London home of Benjamin Franklin, and it is now the only surviving Franklin house in the world ­ a fact that makes it an object of very special veneration for historically minded Americans. When the project is completed, the house will be a living museum to that polymathic figure, in which visitors will learn about his life and ideas by means of a carefully mediated bit of time-travel.

It wouldn't be quite true to say that there isn't a straight line in the building, because down in the basement, behind the original kitchen, a small modern seminar room has been constructed as a space where visitors will begin their tour. It was here that the trust got its first surprise, when excavations of the basement uncovered a bone pit filled with some 1200 fragments of human remains. These are thought to be the residue of the anatomy classes run in the house by William Hewson, husband of the daughter of Franklin's landlady ­ a business which may well have drawn on a steady supply of raw material from the hangings which were held every Saturday just up the street at Charing Cross. The bone pit also contained turtle bones and mercury, the detritus of an investigation into the lymphatic system which won Hewson one of the Royal Society's Copley Medals.

"I've never felt any bad spirits down here", Balisciano says, but, as the tour continues, it becomes clear that something has possessed her ­ whether it's the house or the ghost of Franklin himself. She positively effervesces Frankliniana like a well-shaken champagne bottle ­ every room provoking a fresh surge of anecdotes and explanations. It is her job to be contagious in this enthusiasm ­ since it usually falls to her to take potential supporters round the building ­ and it has to be said that it is a job she does well. It isn't very long before you've been persuaded that what she describes as "the first de facto American embassy" must have been a very remarkable place in its heydey.

Franklin had come to London as an agent for Pennsylvania, hoping to persuade the Penn family to take their stewardship of the colony more seriously or, alternatively, to get the King to take over the colony by a form of nationalisation. He was, it turns out, a somewhat reluctant republican ­ Anglophile and loyalist by inclination and only reluctantly coming to the conclusion that divorce was the only solution. For 16 years he was exploring the alternatives to revolution, not preparing for it. And he was doing an astounding number of other things too, many of which will be represented in the fugitive drama which the trust have in mind for their first paying visitors.

Tours will take place at night, by candlelight, and will notionally be conducted by Polly Stevenson, the landlady's daughter and a woman who ended up so close to Franklin that she eventually moved to America and was with him when he died.

As visitors move round the house, Franklin himself will be close but never entirely graspable, heard reading from his letters in the next room, or from The Craven Street Gazette, a playful spoof newspaper which he wrote for the amusement of his landlady and fellow lodgers. How he found the time for such diversions is mystifying because as well as acting as London agent for several American states, swimming in the Thames, making clean copies of all his correspondence and entertaining guests such as Thomas Paine, Adam Smith and David Hume, he was also continuing the scientific experiments which had already made him famous and was even dabbling in invention.

The house will contain an example of the Franklin stove ­ a Kyoto-compliant design which increased heating efficiency and decreased pollution ­ and visitors will enter his upstairs parlour to the unearthly sounds of the glass armonica, a musical instrument Franklin designed after being enchanted by someone playing tunes on the rims of wine glasses.

There is the odd moment when I wonder whether Marcia's passion for this great man has got the better of her ­ most notably when she credits him with the invention of the StairMaster because he used the Craven Street stairs for exercise and recorded the changes in his pulse as he did so. I think she is joking at this point, but I can't be entirely sure ­ and I couldn't blame her even if she wasn't.

By the time we reach the attic ­ which will eventually become a study centre allowing schoolchildren to conduct hands-on experiments on the problems Franklin himself studied ­ I am beginning to succumb to Benmania myself. It is a life of wonderful gusto and engagement, marked throughout by a mischievous sense of humour; it's easy to believe the apocryphal story that he would have been invited to draft the Declaration of Independence but for the fear that he would stick a joke in.

It's also easy to understand why President Clinton should have designated the Craven Street house as an American Treasure ­ the first foreign structure to be given the title. They have a way to go yet, but the signs are that it will be an English one, too.

The Benjamin Franklin House is at 36 Craven St, London, WC2N 5NG (020-7930 9121)