London Mayor Ken Livingstone wants a complete ban on the importation, manufacture and sale of replica guns - and he has the support of the Metropolitan police.

Mr Livingstone believes proposals in the Government Anti-Social Behaviour Bill have not gone far enough.

Under the proposed legislation there is a mandatory five year ban on possession of a firearm and new powers of arrest for having an air weapon or imitation firearms in a public place without lawful authority or reasonable excuse.

The legislation will also prohibit the importation, sale or transfer of firearms which use a self contained air cartridge system.

The mayor's policy director for policing, Lee Jasper, said even after consulation with the Mayor and police the government had failed to see the "replica gun" loophole in the proposed legislation.

The Mayor is deeply concerned about the availablity of replicas being bought in high street stores, or over the internet, and converted into powerful weapons.

There are estimated to be 500,000 replica guns in circulation in the UK.

It "defies belief" replica guns could be bought with absolute ease and easily transformed into a deadly weapon, Mr Jaspers said.

A Metropolitan Police spokesman said the Met - which took a hard nose apprach against those who committed gun crime - fully supported the Mayor's campaign.

For victims it was almost impossible to identify a real gun from a replica. This included officers who were faced with making quick judgements.

A replica could be picked up for as little as £50. It took as little as ten minutes in some cases to convert a fake into a real gun, he said.

In the past few months police have arrested a number of people involved in gun conversion factories.

During the month long gun amnesty, held earlier this year, a total of 3,189 firearms were surrendered to police. Of this total 776 were imitation firearms including blank and non firing weapons, including BB guns and deactivations.

About 70 per cent of firearms offences investigated by Operation Trident are carried out using a converted replica firearm.

Under the proposal all replica guns and anything which looked like one would be banned.

This included the cigarette lighter Derek Bennett was carrying when he was shot dead by police. Officers fired six shots at Mr Bennett as they thought he was brandishing a weapon which, it emerged, was a gun-shaped cigarette lighter.

Detective Superintendent Sharon Kerr said the benchmark would be 'does it look like a firearm or is it capable of being converted into a firearm'.