More than half a million serial criminals have been let off with repeated cautions, it was disclosed yesterday.

Tens of thousands of the offenders have been given four or more formal warnings since 2000, figures obtained by the Tories show.

It means burglars, muggers, violent attackers and other criminals continually avoid court and the risk of jail despite committing more and more crimes.

Thousands are even receiving repeat cautions in the same year and the proportion is growing.

Last year, Home Office guidance told police that an offender could be handed one caution after another if they commit the same "trivial'' offence, provided two years had passed between them.

A total of 2.2 million people were handed a caution between 2000 and 2008, including 554,247 who were given at least two over the period, the figures show. Of those, 51,874 were cautioned on four separate occasions and 104,915 three times.

David Ruffley, the shadow policing minister, said: "This is a scandal. It sends out the wrong message to career criminals. A repeated slap on the wrist will not deter people from going on to commit more crimes.''

Over the eight years, 23,588 people have received four or more cautions in a single year.

The Director of Public Prosecutions has called for an overhaul of the way cautions are used to punish violent offenders. Freedom of Information requests by the BBC's Panorama programme found that last year police handed out nearly 39,000 cautions to people accused of actual bodily harm.

Keir Starmer tells the programme: "I accept that what is needed is a coherent system across the board with one overarching scheme.''