Payments to informers by London police total about £5,000 a day.

Scotland Yard paid £1,863,074 in rewards for information about criminals operating in London and across Britain during the last financial year, and £2,131,786 over the previous 12 months.

The Metropolitan Police, like other forces in England and Wales, refuses to disclose its spending on informants even after Freedom of Information requests. However, the new figures were obtained by the Press Association from budget documents filed at the end of the financial year 2008-2009.

They revealed that a further £156,469 was spent on “informant related expenditure”, believed to include travel, accommodation and meals for police handlers.

The documents also show that £3,389,950 was spent on secret surveillance operations against organised criminal gangs and terrorists. The figure was made up of a £1,636,365 bill for covert operations, £489,604 for covert terrorist operations and £1,263,981 on covert running costs.

Senior officers have said that despite huge advances in surveillance technology, informers remain a key weapon against the most dangerous villains. Informants — known to police as “covert human intelligence sources” — are particularly cost effective when compared with the price of arduous surveillance operations and other tactics.

There is evidence that MI5 shares this view and has redoubled its efforts in recent years to recruit informants, particularly in the fight against Islamist terrorism.

However, critics fear that informant handling procedures could be abused by officers because large amounts of cash change hands under a cloak of secrecy. Members of the Metropolitan Police Authority, the force’s board of governors, have met behind closed doors over the past 12 months to discuss the matter.

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