Counter-terrorism officers have reportedly started asking their informants to take lie detector tests in a bid to improve the quality of intelligence.

Sources who work with the police will face polygraph examinations under an initiative recently launched by Scotland Yard.

The rigorous questioning is designed to help detectives spot misinformation from informants whose integrity is in doubt due to their criminal associates and background.

It will be overseen by the Metropolitan Police’s assistant commissioner Mark Rowley, who leads national counter-terror policy, according to The Sunday Times.

Questions have been raised over the reliability of MI5 and police intelligence following a spate of terrorist attacks in the UK that left 36 people dead over the last four months.

The security services are reviewing their procedures at the request of Theresa May after it emerged that they were warned repeatedly about Manchester bomber Salman Abedi, who had links to the Libyan Islamic Fighting Group, an al-Qaeda affiliate.

The Prime Minister also wants to weaken encryption and increase censorship on the internet, and plans to force technology firms to allow spies and agencies read everyone’s private communications.

She has accused internet companies of providing terrorists with “safe spaces” where they can upload extremist content.

Theresa May: We do need to have international regulations in cyber space to stop terrorism

Police and security services have pointed to a lack of resources as they take on an unprecedented terror threat from Isis.

Ms May is to make cutting off funding for terrorists the centrepiece of her G20 negotiating goals, and is set to urge the international community to crack down on “permissive environments for terrorist financing”.

Speaking ahead of the G20 summit, the Prime Minister said: “We know that the terrorist threat is evolving. We have seen the threat spread out of Syria and Iraq – into other countries and online.

G20 Protesters take Hamburg Show all 8 1 /8 G20 Protesters take Hamburg G20 Protesters take Hamburg German riot police use water cannons against protesters during the demonstration during the G20 summit in Hamburg, Germany REUTERS G20 Protesters take Hamburg German riot police clash with protesters during the demonstrations during the G20 summit in Hamburg, Germany REUTERS G20 Protesters take Hamburg Riot police move in through the smoke from a smoke bomb during the "Welcome to Hell" rally against the G20 summit in Hamburg, northern Germany AFP/Getty Images G20 Protesters take Hamburg Riot police use water cannon to put of burning bins as a protester runs off after the "Welcome to Hell" rally against the G20 summit in Hamburg, northern Germany AFP/Getty Images G20 Protesters take Hamburg Protesters throw beer bottles as they shield themselves from water cannon spray during the "Welcome to Hell" rally against the G20 summit in Hamburg, northern Germany AFP/Getty Images G20 Protesters take Hamburg A firefighter works at the scene where a number of cars burnt down during the G20 summit in Hamburg, Germany REUTERS G20 Protesters take Hamburg The interior of a burnt down car is seen as firefighters work in the background during the G20 summit in Hamburg, Germany REUTERS G20 Protesters take Hamburg German police remove a protestor who is blocking a street at a demonstration during the G20 summit in Hamburg, Germany REUTERS

“As we deny physical space to terrorists to operate in theatre, we must outpace the terrorist methodology as it develops to attack other vulnerable targets and increases inspired attacks.

“We must therefore combat the threat from every angle. This includes taking measures against permissive environments for terrorist financing, and monitoring the dispersal of foreign fighters from battle.