Dickens wrote the book during six crazy weeks in 1843, when he "wept and laughed and wept again, and walked about the back streets of London long after good sober folks had gone to bed." You can still walk the same back streets today.
I joined a Sunday morning walk from Tower Hill. Our guide, June Street, stood on a stone platform beside a section of Roman wall and with a series of theatrical flourishes, and a chorus of oohs and aahs from visiting Americans, told the tale of "the most famous ghost story ever written".
Heading down Pepys Street, we came to St Olave's church, where Samuel Pepys would come to atone for his numerous affairs and where he is buried beside his long-suffering wife. Dickens loved this churchyard, with its skull and crossbones over the gate - "the churchyard of St Ghastly Grim", he called it, "with the attraction of repulsion".
Turning right along Seething Lane and crossing Fenchurch Street, we soon reached Leadenhall Street and Richard Rogers' Lloyds building ("like an oil refinery that has got lost", opined June). In Dickens' day this was the East India Company, from where an empire was run. Passing behind Lloyds along Lime Street, we came to Leadenhall Place, where a market has been held since Roman times.
Dickens wrote in Nicholas Nickleby that there was no point in living in the country when you could get newly-laid eggs each morning at Leadenhall. The handsome Victorian ironwork now shelters wine bars and oyster stalls but the butchers' hooks which once held swans and peacocks for the Christmas table are still there - and the butcher is still called Butcher. Perhaps this was where Scrooge dispatched a young boy on Christmas morning to buy the prize turkey for Bob Cratchit's family; perhaps the nearby Croissant Express was the baker's shop where Mrs Cratchit had her goose cooked.
From here it is a short walk to Cornhill and the heart of Dickens' tale. We know that Scrooge's counting-house was on a courtyard in the vicinity of Cornhill, facing "the ancient tower of a church, whose gruffold bell was always peeping down at Scrooge out of a Gothic window in the wall." Facing the church of St Michael Cornhill is Newman's Court. Is this where Scrooge dismissed his clerk on Christmas Eve with a grudging: "You'll be wanting the whole day tomorrow, I suppose"?
Cratchit, we are told, slid down a frozen Cornhill "in honour of Christmas Eve" before racing home across the fields to Camden Town; Scrooge, meanwhile, "took his usual melancholy dinner in his usual melancholy tavern." There are several possible candidates. Along St Michael's Alley beside the church, the Jamaica Wine House stands on the site of London's oldest coffee house; near here is the George and Vulture, where Dickens once stayed, and where his character Mr Pickwick lodged while being sued by his landlady for breach of promise. But the tavern which Dickens had in mind may well have been Simpson's, which opened in 1757 in nearby Ball Court and is still open today, though hopefully a little less melancholy.
Back in Cornhill, a left turn brought us to those great counting-houses, the Bank of England and the Royal Exchange, whose dealers Scrooge heard in his dream dismissing his death as they "hurried up and down and chinked the money in their pockets". Times have changed - doubtless many of the clerks will be taking two weeks off for Christmas, instead of the single day begrudged to Cratchit by Scrooge. Across the street is the Mansion House, still home to the Lord Mayor of London, who in Dickens' story "kept Christmas as a Lord Mayor's household should", and probably still does.
Soon we came to Cheapside, once known as West Cheap market, which surely would have appealed to Scrooge. The names of side streets reveal the character of this old London souk - with Poultry, Bread Street and Milk Street, you could almost buy a whole Christmas dinner here. Halfway along Cheapside, the church of St Mary-le-Bow rings out with the Bow bells, the ones which define a person's Cockney status - though barring accidents, you are unlikely to be born within earshot these days.
The walk ended at St Paul's Cathedral, which once stood out from its surroundings so much that Bob Cratchit used its dome to guide his way to work. Now it is dwarfed by the temples of money and power. What would Scrooge have made of that?
"God bless us every one," said June Street, echoing the words of Tiny Tim, as she sent us off into the icy afternoon with Christmas spirit renewed.
q London Walks (0171 624 3978) has Dickens' Christmas Carol walks from Tower Hill tube station at 2pm today (21 Dec), Christmas Eve, Boxing Day and New Year's Day, and at 11am on 28 Dec and 4 Jan. No need to book; just turn up. The walk lasts two hours and costs pounds 4. 50.