HE'S got “a bit of a Boy's Own job” - riding bikes, driving cars and carrying guns as a member of the Royal Protection team. He helps safeguard VIPs - including the Queen and the Prime Minister - and escorts between courts and prisons defendants facing terrorism charges.

HE'S got “a bit of a Boy's Own job” - riding bikes, driving cars and carrying guns as a member of the Royal Protection team.

He helps safeguard VIPs - including the Queen and the Prime Minister - and escorts between courts and prisons defendants facing terrorism charges.

On his loo wall is a framed, handwritten, “get well soon” note from Tony Blair. The PM sent it about a year ago after a careless driver knocked Bryan Lightbody off his motorbike during an escort duty. The policeman suffered bumps and bruises that kept him off work for about five days.

To we mere mortals it all sounds very glamorous, scrapes and scratches excepted. And it is. But when he's not watching a politician's back, Bryan's thoughts often stray to the London of the 1880s and a series of killings that continues to tease our sense of the mysterious. Labelled the Whitechapel Murders, they are said to have been committed by a fugitive nicknamed Jack the Ripper.

Bryan joined the Metropolitan Police in 1988, by chance the centenary of the murders, and his interest grew over the years - fanned by the books on the market, the regular theories that popped up, and films.

Perhaps, he came to think a decade or so later, he might be able to write a book himself - not an academic study but a period thriller based on the case and the major investigation that drew a blank.

The result is Whitechapel, his 178,000-word tome. With the crimes of autumn 1888 at its heart, it's also a story of love, duty, romance, tragedy and revenge that links London with Paris and Missouri. It's self-published, but Bryan hopes his work might attract the eye of a publisher or agent.

In the book he plumps for a murderer - hypothetically, of course. It's one of the names regularly put forward by Ripper theorists, but we won't spoil the surprise here by revealing it.

A large number of suspects have been in the frame over the years - some more likely candidates than others.

“If you take, for example, Murder by Decree, the film in the late 1970s with Christopher Plummer” - playing Sherlock Holmes - “Jack the Ripper with Michael Caine, and From Hell (a 2001 film starring Johnny Depp) they all point to this Masonic/royal conspiracy, with Sir William Gull (physician to Queen Victoria) as being the murderer.”

Bryan doesn't buy that idea.

“Well, I just don't think physically he'd have been able to do it, because he'd suffered a stroke. Something about it I've never found terribly convincing.

Patricia Cornwell spent a lot of money on an investigation, and in a subsequent book named her chosen killer. “But I think the guys that produced the evidence against (his chosen guilty man) put together a really good, strong case, with a lot of credibility. He is a strong, if not the strongest, suspect. He's not the only one - there's compelling evidence against other people.”

Patricia Cornwell's quest reportedly cost more than £3million, including the hiring of forensic scientists. Her book - Portrait of a Killer, Jack the Ripper: Case Closed - accused British Impressionist artist Walter Sickert, though many other Ripper historians pooh-poohed her claim. In 2005 she was moved to take out full-page adverts in two national newspapers to refute suggestions she was obsessed with Jack the Ripper.

It's by no means definite how many women were killed by the same hand, adds Bryan. There were five “canonical” - so-called authoritative - victims: Mary Ann “Polly” Nichols, “Dark Annie” Chapman, Swedish-born Elizabeth Stride, Catherine Eddowes and Mary Jane “Ginger” Kelly.

“Well, I think only four of them were murdered by the same person.” At least one victim, “Long Liz” Stride, wasn't mutilated in the same way as the others.

The Whitechapel Murders are indeed an enduring enigma, “and I think that is the draw for most people - because nobody knows.”

He does, though, find it amazing the perpetrator wasn't caught - and especially that the police didn't stumble across him in the act.

Bryan's read that 1,400 or 1,500 constables were then based at a handful of police station in east London. “OK, they were working different shifts; but that's more than there is now! You think that with all those, and detectives, and people drafted in, and plain-clothes patrols, how come no-one found him?”

That failure has helped feed the suspicion the authorities simply must have colluded in a cover-up.

“We do live in a world of conspiracy theories - and, I've got to say, I take great interest in them! But I just think that if they've tried to cover up anything with Jack the Ripper, perhaps all it is is ineptitude. Perhaps it was missed opportunities.

“I'm not a great believer in the story that Prince Albert Victor” - the Duke of Clarence - “had an illegal, secret marriage to a Catholic woman and fathered a child, and the only people who knew were five prostitutes who were all murdered as a result. And so it stops as soon as it began.

“It's a great romantic story; but it was just a depraved killer whose fury became worse - as most modern serial killers' does.”

Bryan's approach was partly inspired by Anthony Grey's novel Saigon, which follows the life of Joseph Sherman from the time he arrives in the city in 1925, as a teenager, to his final departure when the Americans withdraw in 1975. “I liked the idea of using a true story and weaving some fictional characters. I thought I could do that with the Ripper.”

His time as a traffic patrol officer in the 1990s, working out of Bow, helped provide a sense of atmosphere.

“When you were working night duty, you would creep around different parts of the East End in the early hours, and quite often I'd find myself around Shoreditch and Whitechapel, and off Commercial Road and Bethnal Green, and it gave a sense of what it would have been like.

“There are a lot of streets there that are as were. If it was quiet and you turned the engine off and went to have a look around - maybe under some railway arches - you did get a sense of what it might have been like, because the buildings are effectively the same.”

In fact, in some ways life goes on in very similar fashion to 1888. The area has traditionally had a transient, shifting population, he says. Whereas problems used to be fuelled by alcohol, now it's drugs. Similarly, street gangs and turf wars are nothing new; instead of yesteryear's flat caps and scarves, contemporary gang uniform features hoodies.

Terrorism is not a solely-modern phenomenon, either. In the 1860s and 1870s London saw attacks by Irish-American groups. Six people were killed in Clerkenwell, for instance. The Home Office, the House of Commons and Scotland Yard were also targeted. As Bryan says: “There are many parallels with today's society.”

When it came to writing, he didn't find it too difficult to hit the right spot with his dialogue.

“I tried to avoid cliché. And it's only 100 years ago; the way people spoke wasn't that much different. In fact, many people then were probably more articulate than now!”

He smiles at the thought of one episode: a drunken prostitute's rant.

“Having worked in the East End and seen people lose it, and having listened to their tirades, I know exactly how people talk! Every time I read that bit, it makes me laugh.”

There's been “a massive amount” of interest from colleagues in the Met. One or two have had surprising queries, such as why he killed off a paperboy. “I had to say 'Well, it's relevant to the plot!'”

Whitechapel is available on www.amazon.co.uk, www.authorhouse.co.uk, at Hannays bookstore in Braintree, or via bookshops by giving the ISBN number: 978-1-4259-6181-7

AT the centre of Whitechapel (the book) is an astute Victorian constable called Robert Ford. If Bryan Lightbody has his way, it won't be the last we hear of the fictional policeman.

The author's about 100 pages into his second book. It's a fictional political scandal set in Edwardian London, 15 years on from the Ripper murders. Ford is now a detective inspector, working as a protection officer.

Bryan's also brewing a third tale - set another decade on and destined to see out Ford's career. He'll probably be a detective chief superintendent by then, and the story will likely lead up to the assassination of Archduke Franz Ferdinand, the heir to the Austrian throne - an event that precipitated the First World War.

He would bite the hand off any publisher interested in his work; and is flummoxed by the fad for books by D-list celebrities. “It would be nice to see someone reading a book of mine on the Tube,” says Bryan, who lives near Braintree with wife Christine, a sergeant in the Met.

He hails from Chadwell Heath. Both his parents were from the East End: his mum, a teacher, from Bow; his dad a policeman from East Ham. Until his mid-teens he was keen on following in his father's footsteps, but then flirted with the idea of joining the forces.

After flunking his A-levels he did clerical work for MI5 while aiming to re-take his exams. During that period he helped out in the aftermath of an accident. The experience rekindled his interest in the police and 13 months later he was at the training college at Hendon.

Bryan's career with the Met now stretches nearly 20 years. He spent five years on the beat in Ilford, did traffic patrol in the East End, served as a car and motorcycle instructor at the police driving school in Hendon, and is now in the Special Escort Group.

The Victorian era is not the only historical period of interest. The film Gladiator got him hooked on the Romans. Bryan even joined a group called Britannia - predominantly a fifth-century Romano-British re-enactment society that was involved in the filming of the opening battle sequence in Gladiator.

Over four or five years he's “fought” as a gladiator and has even got a complete set of first-century imperial legionary kit. “It's funny, because walking around it in isn't that different to walking around in police kit. It's probably as heavy as my ballistic kit at work.”

He's done some big weekend re-enactments for the Museum of London; and in 2003 went out to Italy as part of a warm-up act for a Celebrity Gladiators head-to-head involving former boxers Chris Eubank and Nigel Benn.