Blank firing pistols available to order online from around £100 are being converted into lethal weapons in makeshift factories across the UK, police have warned.

Officers from the Metropolitan Police said that illegal workshops have been set up in a number of areas to change the weapons into live-firing guns and make ammunition to fit them.

One of the most common types is the Turkish Retay pistol, that can be legally imported and owned in the UK in its blank firing state.

Detective Superintendent Nick Blackburn from the Met’s Specialist Crime Command said: “We’re seeing a rise in the number of converted blank firing weapons that we recover.

“Most notably we’ve seen a rise in Retay pistols which have Turkish origin. These pistols can be converted with relatively basic knowledge and made into a lethal-barrelled weapon using converted ammunition.”

He went on: “We have uncovered several factories in London, in Manchester, and in other areas of the UK as well.

“It’s a problem UK wide not just in London, other forces are reporting the same kind of findings with Retay pistols in particular.”

Police and UK law enforcement are in talks with manufacturers to make the pistols harder to convert, and want possession either made illegal or placed under tighter controls.

Some UK athletics clubs have already agreed to stop using certain kinds of starting pistol after talks with police.

Mr Blackburn said: “We are currently working with colleagues from the Border Force and the National Crime Agency to appeal to manufacturers of convertible blank firers to build in systems that would make it far harder to convert this type of weapon.

He added: “People are importing these legally. There are people intent on converting them and making ammunition for a live firing weapon and they are finding their way into the hands of organised crime groups.”

Senior officers want to see changes to the law around blank firing pistols.

Met Commander Dave McLaren said: “This is an emerging trend and we are constantly looking at new powers and legislation that might support us in this fight against gun crime.

“This is one area in particular I’m really focused on seeing what we can do to make the holding of those blank firers illegal or certainly controlled in some way.”

Last summer when lockdown restrictions were eased there was an increase in violence in London, including in July the highest number of incidents where a gun was fired since 2018.

The Met launched a fresh crackdown on gun crime in early March, Operation Elie, in a bid to prevent a similar spike this year.

Force figures show that 366 lethal barrelled weapons were seized in 2019, 443 in 2020 and 56 in 2021 (up to April 28). The number of times they were fired went from 281 in 2019/20, to 266 in 2020/21.

The Met said while the number of gun deaths went from 11 in 2019 to 15 in 2020, in the past six months there has been only one fatality in the capital.

Among the seizures, the number of handguns captured by police rose from 155 in 2019, to 269 in 2020. Officers have captured 56 up to April 28 this year.

The rise between 2019 and 2020 is being put down to the success of a major international sting, Operation Venetic, after an encrypted phone network used by organised criminals was successfully hacked by law enforcement in France.

The number of submachine guns seized in London has stayed low: 3 in 2019, 2 in 2020 and 2 up to April 28 in 2021.

The pair seized this year were discovered when officers stopped David Longhor, 19, near Chiswick Park tube station on March 2 and found two Skorpion submachine guns in his rucksack along with 40 rounds of ammunition.

Longhor, of Villiers Road, Ealing, west London, said he was carrying the guns for someone else in order to repay a debt.

He admitted two counts of possession of a firearm and one count of possession of ammunition and is due to be sentenced at Isleworth Crown Court on June 4.

Police said the firearms are capable of firing 14 rounds per second and have “significant capacity to harm”.