THE tour guide warned us in advance. "Anything can happen on the next part of the walk," he said, as we moved from the prosperous City of London into the seedier East End.

We were walking in the footsteps of Jack the Ripper, the infamous serial killer who terrorised Victorian London with bloody slayings and mutilations of local prostitutes in the autumn of 1888.

Guide Donald Rumblelow, former policeman and author of The Complete Jack the Ripper, told us of things to expect on the next leg of the hour-long trek.

In the past, prostitutes have mingled with walkers trying to pick up custom. Drunks have joined the tour, adding alcohol-fuelled footnotes to the official commentary. Once, a man appeared in a window, wearing a basque, stockings - and nothing else. One night, a chap was seen tap-dancing on the roof of a moving car.

Our incident happened on a dark, deserted street of shops opposite a store selling pump-up bras ("enhance your cleavage for £7.99"). As we stood listening to Rumblelow recount the gory details of a Ripper killing, several men carried boxes from a nearby electronics shop. They could have been robbing the place for all we knew.

A police car drove down the road slowly and stopped briefly, engine still running, while observing a group of youths prowling at the end of the street.

The law drove off. The youths did not. Rumbelow's commentary was interrupted by the sound of missiles being thrown at our group. "They're throwing bricks," observed one of our number. Rumbelow decided the wisest course was to move on quickly.

None of this could have been predicted as our band of walkers assembled outside Tower Hill Underground station in the shadow of the Tower of London to follow the Ripper's trail. We were a group of journalists, film publicists, Cloak and Dagger Society members, and even the official biographer of Queen Victoria's surgeon and prime Ripper suspect, Sir William Withey Gull.

The publicity people at Twentieth Century Fox arranged the walk to coincide with the opening of the new Jack the Ripper movie From Hell. We were walking not only in the footsteps of the killer, but also of American actor Johnny Depp. He took the walk incognito as part of his research for the film in which he plays the drug-addicted police inspector trying to catch the Ripper.

Rumbelow was impressed by his star walker. "He's one of the best informed people I've guided," he says. "He's intelligent, easy to get on with, genuinely nice. He'd read my book, which was flattering."

From Hell was actually filmed in Prague, after the American directors, brothers Allen and Albert Hughes, rejected the idea of shooting in the East End. "London was the first choice, but it's hard to shut down for filming," they explain.

They went to Prague, only to find the buildings there wouldn't double for Victorian London. So Whitechapel was built in the middle of a field outside the Czech capital. Production designer Martin Childs based his designs on hundreds of photographs and detailed drawings. The finishing touch was hundreds of centuries-old cobblestones borrowed from local breweries and civic institutions. They had to be returned at the end of filming.

Commerce Street, Christ Church, the Ten Bells public house and specific scenes of the Ripper's crimes were recreated. Two British painters were recruited to ensure the proper colouring and ageing of the set's exterior.

Robbie Coltrane, who plays Depp's policeman sidekick on screen, says: "When I first saw the set it was one of the greatest experiences of my life. There were two complete streets of Whitechapel. You wouldn't know it's not real. The set was quite spectacular."

Back at the real thing, Rumbelow is impressing us with his knowledge of the Ripper, his murders and the crime scenes as we tread the deserted streets around the famous Petticoat Lane market. He lives up to his billing as being "internationally recognised as the leading authority of Jack the Ripper".

The murders are recounted in grisly detail. The Whitechapel murderer stabbed and gutted five prostitutes within the space of four months. He earned his Jack the Ripper label from the signatory of a letter and postcard sent to the Central News press agency. George Lusk, chairman of the Whitechapel Vigilance Committee, received a less pleasant gift - a parcel containing half a kidney and a letter headed "From Hell".

As we stand on the scene of each murder, Rumbelow tells us the background to the attacks, and details what the Ripper did to the bodies, conjuring up the grim atmosphere of those times. Prostitutes were generally older women who lived and worked on the streets of Whitechapel. Many had drink problems.

Poor street lighting and foggy London nights made it easy for a killer to strike and make his escape unnoticed. The Ripper operated over two different police districts, causing confusion between the two.

Unless a killer was caught in the act, the chances of arrest were slim in the days before fingerprint evidence was introduced. The Ripper was lucky in Mitre Square. The body of victim Catherine Eddowes was still warm, suggesting he'd only just struck.

Rumblelow lists the prime suspects. Some say the Ripper came from the royal family. Others claim he was a mason, who was protected by fellow members of the secret society. A third suspect is Queen Victoria's physician.

Much of the area remains pretty much the same, except for the Spitalfields area, home of the old fruit and vegetable market. This is now a regeneration area with millions of pounds being spent on restoration and new buildings. Loft apartments are being created, with a top price of £750,000.

We end the tour at the 200-year-old Ten Bells pub, haunt of prostitutes in Victorian times. Perhaps Jack the Ripper drank there. Johnny Depp certainly did, stopping for a couple of halves of lager at the end of his walk.

There are those who say that, horrific as his crimes were, some good came of Jack the Ripper's activities. His crimes drew attention to the awful living conditions in the East End slums and led to their demolition. It's been said that he did more to change the face of the East End than half a century of agitation by reformers. "He was a social worker with a knife," says Rumbelow.

* From Hell (18) is showing in cinemas now.