George Galloway will not face a criminal investigation by Scotland Yard into allegations he broke United Nations sanctions by taking oil money from Saddam Hussein, The Herald can reveal.

The Metropolitan Police, after liaising with the Crown Prosecution Service, has dropped any idea of investigating claims of corruption against the 52-year-old anti-war Respect MP, or anyone else, and has handed the file back to the Serious Fraud Office (SFO).

It is thought it would be better for a single agency to investigate allegations involving the discredited UN oil-for-food (OFF) programme. While the SFO has decided to expand its £22m probe into alleged fraud concerning humanitarian aid contracts to take in oil contracts, it made clear Mr Galloway, who has consistently denied any wrongdoing, would not figure in investigations.

A spokesman for the SFO said: "For us to get involved, it would have to involve a complex fraud inquiry. In relation to Mr Galloway, he does not come within the scope of our inquiry." He explained this was because the claims against the MP did not involve complex fraud - but corruption.

The SFO, however, did reveal that, following talks with Scotland Yard, its inquiry, the existence of which was exclusively revealed in The Herald last month, has now been "expanded to include not just the humanitarian contracts but oil contracts as well". No individuals were being investigated - only companies.

Last night, Mr Galloway, the MP for Bethnal Green and Bow in east London, was unavailable for comment. However, Ron Mackay, his spokesman, said the decision not to investigate the back bencher came as no surprise. "He's had no contact or e-mail, not a visit, not an inquiry by anyone in an official position - be it the SFO or Scotland Yard. It's a complete utter non-event," he said.

In May 2005, Mr Galloway testified before the US Senate investigations subcommittee and denied the OFF programme allegations against him, declaring: "I have never seen a barrel of oil, never bought one, never sold one, and neither has anyone on my behalf."

The former Glasgow MP will not be investigated by either Scotland Yard or the SFO, but Sir Philip Mawer, Westminster's parliamentary commissioner, is still looking into whether, in light of the OFF programme allegations, Mr Galloway breached any Commons rules.

Furthermore, the Charity Commission is continuing its inquiry into the Mariam Appeal, the £1m political fund set up by the Respect leader, to see if it received any funds via the OFF programme and, if so, whether they were right and proper. It's thought the SFO will target those companies whose names appeared in the UN report of 2005, which accused various organisations of taking kickbacks under the OFF programme.

The report by Paul Volcker, a former chairman of the US Federal Reserve, claimed the OFF programme, under which Iraq could sell oil to buy food and medicine, had become riddled with corruption as Saddam's government demanded kickbacks totalling £1bn from foreign firms in return for the oil contracts.

Almost 2400 companies worldwide were linked to allegations of bribery, including 11 from the UK, all of which have denied any wrongdoing.