Scotland Yard is to enlist terrorist convicts and other former extremists in a new bid to combat Islamic State propaganda and stop more Londoners being lured to fight in Syria.

Chiefs want to develop new “counter-narratives” to challenge Islamist ideology. The plan has already involved using militants who have returned after travelling to join conflicts abroad.

Police say their attempts to stop the spread of radical ideas are receiving “significant” help from these people — and they are “desperate” to recruit more. Met officers are also seeking to “turn” terrorist convicts freed from sentences, and others still in jail, in a further bid to find new ways to persuade young Londoners to shun extremism.

The moves — amid continuing official concern at the number of Britons radicalised by IS propaganda — were revealed today by Commander Richard Walton, the Yard’s head of counter-terrorism, in an exclusive interview with the Standard.

In a series of wide-ranging comments, Commander Walton also:

Disclosed that the Met rescued several families, some including toddlers, heading to Syria from Turkey in recent months after tip-offs by “loved ones” worried about their fate.

Praised a “shift in the mindset” of London Muslims which gave police vital help in the fight against extremism.

Announced a 32 per cent rise in London counter-terrorism arrests over the past year, with 225 people held in the 12 months since last August. Those who have been arrested include 29 female suspects and 17 teenagers, of whom five were girls.

Told of police concern at radicalisation in jails, saying a “lot more” could be done to tackle extremism there.

His most significant disclosure, however, centred on the Yard’s efforts to seek support from ex-jihadis who have abandoned radicalism. “They are the most powerful voices,” he said.

“We have a few, not many, but those we have are significant. It’s not necessarily Syria, we have others back from Afghanistan — al Qaeda related. We are desperate to find more.”

He said the recruitment of jihadis who had gone to Syria was difficult as “most don’t come back” but added that repentant extremists in this country offered an equally valuable alternative.

“We’re more likely to have success, as we do, with those who have been radicalised here and those who have been to prison,” he said.

“We can’t write off anyone convicted of a terrorist offence. We have got to try to work with them, engage with them, in prison if necessary, and try to turn them around.

“Some terrorist offence sentences for possession of extremist material are not lengthy. We know they are going to come out. It’s a concerning offence but they’ve not gone on to commit more serious terrorist offences, so there is an opportunity to work with them.

“A lot more could be done in that area. There has been some success on that. We talk to people in prison and when they come out.”

Commander Walton added that des- pite such efforts, radicalisation in UK prisons posed an increasing problem because police had to launch counter-terrorism operations to tackle plots being developed behind bars. He added: “We are convicting more people, so the challenge in prisons is bigger.

“Where operations start from within prison or with somebody who has just been released from jail, you know there wasn’t much success in de-radicalising them when they were in.

“There has to be more we can do. The issue of radicalisation in prisons is a concern. Everybody needs to think what more can be done.”

His comments today follow earlier warnings by police and the intelligence agencies about the heightened security risk posed by the Syria conflict and the continuing appeal of other terrorist organisations such as al Qaeda.

That risk prompted a surge in arrests and the departure of at least 700 Britons — and potentially many more — to join the wars in Syria and Iraq. About half are estimated to have returned.

Today’s new figures, which show a total of 396 arrests and 186 terrorism-related charges in the capital over the past two years, indicate that the problems are undiminished.

Police emphasise that any ex-jihadi recruited to help counter radical narratives will be carefully vetted to ensure that they have genuinely abandoned extremist ideas.@martinbentham