The Press Complaints Commission is to investigate whether the Sun broke rules over payments to criminals in its dealings with Ronnie Biggs.

Biggs' associates - including convicted Great Train Robbery gang leader Bruce Reynolds - are reported to have been paid �44,000 by the Sun for their help in bringing the convicted robber back to Britain.

The watchdog's rules state that payments to convicted criminals should only be made where there is a legitimate public interest.

A statement issued by the PCC said: "The issues relating to payments by a national newspaper to Ronnie Biggs and his associates raise a number of issues under the newspaper code of practice."

Private jet

It added: "As it has consistently done in the past where ethical matters of this sort are raised under the code, the PCC will conduct an investigation into this matter under its normal procedures."

The Sun paid for a private jet to fly Biggs back to Britain.

A spokesman for the paper said the PCC code's requirements relating to payments to convicted criminals were fully taken into account "before we took the decision to fly Ronnie Biggs home".

He added: "We are, as always, happy to cooperate with the PCC and will be making clear to them the massive public interest in returning a convicted criminal home to face British justice and at no cost to the British taxpayer."

In 1998 the home secretary launched a review of the law after it emerged that child-killer Mary Bell was paid to collaborate on a book about her life.

More recently, a PPC inquiry was launched into The Sunday Times' serialisation of a book by disgraced former Tory minister Jonathan Aitken - who served time in prison for perjury and perverting the course of justice.

The Daily Mail attracted criticism in 1999 after reports that it had offered a six-figure sum for an interview with Nick Leeson, the rogue trader who brought down Barings Bank.