A gunsmith who set up a factory in his garden shed to make murder weapons for gangland Britain will be sentenced to a long term in prison today.

Grant Wilkinson drove a Porsche and entertained his girlfriend in five-star hotels with the profits he made from converting replica machine pistols to fire live ammuntion.

His military-style Mac10s, which became known among inner-city gangs as the “spray and pray” gun, were used in nine London murders, including the shooting last year of Michael Dosunmu, 15. Another was fired in Bradford during the robbery in which PC Sharon Beshenivsky was killed in 2005.

Wilkinson, 34, was convicted at Reading Crown Court yesterday of nine firearm offences.

Scotland Yard said last night that 50 of the 90 Mac10s he is known to have converted had been recovered, most of them in London, but others were found in the Thames Valley area, Birmingham, Southampton and Bristol. A reward has been offered for information leading to the recovery of the 40 guns feared to remain in the hands of criminal gangs.

“There can be no underestimating the impact of Wilkinson’s actions,” said Detective Chief Superintendent George Turner, of Thames Valley Police. “His conversion of imitation weapons allowed criminals to arm themselves with guns capable of killing and maiming people.

“Gun factories are very rare and this was a significant criminal operation. The Mac10 is purely a military weapon. It is designed for close- combat killing. It is quite obvious that the upsurge in crimes involving Mac10s can be linked to this factory.”

Detective Superintendent Gary Richardson, head of the Metropolitan Police’s Operation Trident squad, which investigates gun crime among the black community, said that some of the murder scenes linked to Wilkinson had been horrific sights. The weapons were crudely engineered conversions that sent deadly bullets flying across a wide area.

“At some of the murder scenes I’ve been to we’ve found bullets 25 metres to the right and left,” Mr Richardson said. “These are very difficult weapons to fire — they jam regularly. And they are very, very difficult to control in the hands of gang members.”

Mr Richardson’s squad had been on Wilkinson’s trail since the end of 2005, when ballistic tests linked a spate of shootings to the same batch of guns. Officers visited Sabre Defence, in Northolt, West London, where Wilkinson had bought the replica weapons for £55,200 in cash, claiming that they were for use in a new James Bond film.

A member of staff was suspicious of the buyer — who gave his name as Gary Wilson when he placed his order in 2004 — and took a mobile phone picture of him. But the image was indistinct and it was not until July last year that Wilkinson’s workshop was discovered by accident.

Tenants of The Briars, a property owned by Wilkinson in Three Mile Cross, near Reading, became curious about the ramshackle sheds at the end of the garden and opened the doors. Inside they found computer-operated lathes, workbenches, firearms and weapon components in one building and what appeared to be a test-firing range in another. Police recovered 2,700 cartridge cases, which they believe had been acquired for the manufacture of home-made ammunition.

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