Grant Wilkinson, 34, worked in a scruffy garden shed to adapt dozens of replica Mac-10 guns into murder weapons which were then sold to some of Britain's most dangerous gangland criminals.

In four years Wilkinson's huge cache of converted weapons was used in eight murders and more than 50 shootings, including the killing of innocent schoolboy Michael Dosunmus in Peckham, London.

Wilkinson used his back garden in Berkshire to create the most productive gun factory ever found by British police.

One of the guns ended up in the hands of the gang who shot dead Pc Beshenivsky in the Universal Express robbery in Bradford in 2005. Although the Mac-10 did not fire the fatal shot, it was discharged at the scene.

Following his conviction yesterday, Wilkinson was today told he must serve a minimum of 11 years. Confiscation proceedings are also now under way to seize any assets Wilkinson amassed on the back of his criminality.

Police last night admitted an estimated 40 weapons were still on the streets and offered a £10,000 reward to find them.

A jury at Reading Crown Court yesterday convicted Wilkinson of a series of offences, including conspiracy to convert an imitation firearm, conspiracy to sell or transfer firearms and ammunition, possession of a firearm with intent to enable another person to endanger life and possessing a prohibited firearm.

His co-defendant, Garry Lewis, 38, of Bourne End, Buckinghamshire, faced the same charges but was cleared of all.

Wilkinson's gun factory was based in two shabby-looking sheds at The Briars in Three Mile Cross, near Reading in Berkshire.

The three-week trial heard how Wilkinson, using the name Grant Wilson, paid £55,000 in cash in July 2004 for 90 blank-firing Mac-10s from a registered gun dealer, claiming they were to be used on the set of the new James Bond film.

The dealer, Guy Savage of Sabre Defence Industries in Middlesex, became suspicious of Wilkinson's "desperately disorganised" behaviour and secretly took his photograph on his mobile phone.

The factory came to light after one of Wilkinson's tenants stumbled upon gun-making equipment and tools.