The Independent (London) -- A register of convicted and suspected hitmen and the techniques used by contract killers is being compiled to help police catch professional murderers. The initiative follows concern at the growing number of contract killings in Britain, estimated to be up to 30 a year. Police experts have drawn up four main categories of "hits" - disputes over the payments of debts or financial dealings; disputes over drugs; domestic arguments between former lovers; and fighting between rival organised crime groups. Investigators are to be urged to concentrate attention on the person who wanted the contract killing carried out, the person who organised the hit, the killer, and who supplied the firearm if one was used. A central intelligence unit is to be set up to co-ordinate and collate information on professional murders and to establish investigative techniques. Advice on how to run undercover operations and protect people being tracked by paid killers is also being compiled. Tips on how to obtain evidence and to examine suspicious deaths will be included, as some contract killings are disguised as road traffic accidents or drug overdoses, a detective said. The Metropolitan Police has estimated that up to 20 professional hitmen are operating from the south-east of England, charging between pounds 1,000 and pounds 20,000 for each murder. Concern is growing at the growing number of contract killings and the use of hitmen to commit professional murders throughout the country, and at the sophisticated techniques being used by the killers. One infamous London hitman, known as "Mad Georgie," is said to be behind 23 murders. He is credited with thinking up the "motorbike hit" in which two men, whose crash helmets cover their faces, use a powerful off-road scrambler motorcycle. The killers will speed up to their target, and the pillion rider will jump off, shooting his victim with a handgun or sawn-off shotgun. The two men then flee on the motorcycle, taking a predetermined route. The plan for the contract killing database follows an approach by the Met's Organised Crime Group to the National Crime Faculty, the centre of excellence and training at the police college at Bramshill, Hampshire. Detective Sergeant Mark Roycroft, from the National Crime Faculty, said: "There is a clear need for a national intelligence database on contract killers and for guidance on best practice in investigations. The need is for a strategic overview of such killers and contract killing in the UK." A seminar held at Bramshill was attended by: experts in contract killings from the National Criminal Intelligence Service; special branches operating at ports and airports; detectives from the Metropolitan Police and from the Merseyside, Lancashire, Hampshire and Kent forces; the Immigration Service; and the Forensic Science Service. Det Sgt Roycroft said: "New human rights legislation will also impact on these investigations. The senior investigating officers in an inquiry or proactive operation face real problems of when to tell the intended victims of contract killers, and how they should be protected. "In many cases, contract killings are not immediately apparent as they are dealt with as road traffic accidents - when the victim is knocked over - or as suicide cases if there has been a poisoning." THE FOUR TYPES OF 'HIT' The drugs dispute - The Essex Three Pat Tate, above, Craig Rolfe and Tony Tucker were criminals who supplied drugs in Essex and East London and were linked to the Ecstasy that killed teenager Leah Betts. In 1995, they were shot by two fellow dealers in a dispute over a shipment of poor cannabis. The gangland feud - Charlie Wilson The former Great Train Robber, 57, was shot at his Marbella villa in 1990, initiating a gangland feud that has since cost several lives. The gunman was never caught, but the getaway car driver, Danny 'Scarface' Roff, was himself the target of a hit in 1997. The financial dispute - Donald Urquhart Graeme West was convicted in 1995 of the murder of millionaire and suspected money launderer Donald Urquhart in Marylebone High Street, central London. West was paid pounds 20,000 for shooting Mr Urquhart in a dispute linked to his financial dealings. The former lover - Barry Trigwell Barry Trigwell, 44, was battered to death in the bath of his home in Sutton Coldfield, West Midlands, in 1995 by two South African hitmen. The hitmen had been hired by his wife, Anne Trigwell, who was imprisoned for life in 1996.