The Metropolitan police paid £1,863,074 in rewards for information about criminals operating in London and across the nation during the last financial year.
The bill is a substantial drop on the outlay to informants, known to police as “covert human intelligence sources”, over the previous 12 months of £2,131,786.
But it still means police officers are handing over about £5,100 every day of the year, some of it to people with strong links to crime themselves.
Critics fear informant handling procedures could be abused by officers because large amounts of cash changes hands under a cloak of secrecy.
The figures shine a rare light on one of the most secretive areas of modern policing.
The Met, like others forces in England and Wales, refuses to disclose its spending on informants, even after Freedom of Information requests.
Senior officers have said despite huge advances in surveillance technology, information from people remains a key weapon against the most dangerous villains.
They have said informants are very cost effective when compared with 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 on Islamic terrorism.
Members of the Metropolitan Police Authority, the force’s board of governors, have met behind closed doors over the last 12 months to discuss the matter.
The new figures were contained in budget documents filed at the end of the financial year 2008-2009.
They revealed a further £156,469 was spent on “informant related expenditure”, believed to include travel, accommodation and meals for police handlers.
The papers also revealed £3,389,860 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.