MI5 is paying Muslim informants for controversial short-term spying missions to help avert terrorist attacks by homegrown Islamist extremists.

Individuals across the UK, including in Manchester and London, are being employed on temporary assignments to acquire intelligence on specific targets, according to sources within the Muslim community. One said that they knew of an informant recently paid £2,000 by the British security services to spy on activities relating to a mosque over a six-week period.

However, the use of payments to gather intelligence prompted warnings that the system risked producing information “corrupted” by the money on offer.

The initiative is being co-ordinated under the government’s official post-9/11 counter-terrorism strategy, specifically the strand known as Pursue, which has an official remit to “stop terrorist attacks in this country and against our interest overseas. This means detecting and investigating threats at the earliest possible stage.”

A source, not from Whitehall but with knowledge of the payments, said: “It’s been driven by the [intelligence] agencies, it’s a network of human resources across the country engaged to effectively spy on specific targets. It’s decent money.”

They did not divulge the number of informants receiving government funding or how much of the agency’s national security budget is allocated to such transactions. However, the use of payments to gather information prompted calls for caution from senior figures in the Muslim community, who warned that such transactions could produce tainted intelligence.

Salman Farsi, spokesman for the East London Mosque, the largest in the UK, said: “We want our national security protected but, as with everything, there needs to be due scrutiny and we need to ensure things are done properly.

“If there’s money on the table, where’s the scrutiny or the oversight to ensure whether someone has not just come up with some fabricated information? Money can corrupt.”

Farsi said that lessons should be learned from the government’s central counter-radicalisation programme, called Prevent, which was introduced following the 7 July bombings, but despite tens of millions of pounds spent and hundreds of initiatives has been criticised for failing to achieve its goals.

“When they started dishing out money, everyone was willing for a bit of money to dish the dirt, make up stuff. There’s good work to be done, but quite frankly you don’t need to send in informants to mosques to find out what’s going on. We need a fresh approach, genuine community engagement,” said Farsi.

Details of the network of informants paid by the security services follows the first live interview with a head of MI5 – director general Andrew Parker – in the 106-year history of the agency, an opportunity that he used to call for more up-to-date surveillance powers.

Days earlier, on Tuesday, the home secretary, Theresa May, met major internet and telecoms companies to seek their support for a new surveillance bill, prompting speculation that the government is preparing a choreographed campaign to revive its controversial snooper’s charter legislation.

Parker, the director-general of MI5, speaking on BBC Radio 4’s Today programme, warned that terrorist plotting against Britain is at its most intense for three decades with six attempts foiled in the past 12 months.

Subsequent reports suggested MI5 and anti-terrorism officers are monitoring more than 3,000 Islamist extremists willing to carry out attacks in Britain. Numbers have escalated since 2013 with the rise of Islamic State in Syria, with more than 700 Britons believed to have joined jihadi groups in the region and 300 thought to have returned to Britain.

Scotland Yard last month revealed that suspects were being held at a rate of more than one a day while a record number of terrorism arrests were made in the past year, eclipsing the previous peak after the 7 July bombings.