THE Metropolitan Police tonight launched an investigation into the row over Labour's disguised donations after intervention from Eastleigh MP Chris Huhne.

The Electoral Commission will submit its formal report to officers tomorrow and Met Police Commissioner Sir Ian Blair said tonight: "The next step is for us to receive and review their referral report."

A spokeswoman for the Electoral Commission said: ''The Electoral Commission has been in dialogue with the Crown Prosecution Service since November 26 and this afternoon held further discussions with the CPS and Metropolitan Police Service.

''The Commission has now decided to refer matters to the MPS for further investigation.

''We would hope to make our formal report to them tomorrow.'' Mr Huhne, a Liberal Democrat leadership contender, had called for a police probe into the secret funding row.

Writing to Mr Huhne, Sir Ian said: ''Matters relating to the donations to political parties are dealt with, in the first instance, by the Electoral Commission. The CPS and the Electoral Commission have been in dialogue with us this afternoon.

''The Electoral Commission has now decided to refer matters to the MPS for further investigation.

''The next step is for us to receive and review their referral report.'' The move means the nightmare of another police investigation into Labour finances returns to haunt Downing Street just months after the cash-for-honours inquiry ended without charges being brought.

A spokesman for Prime Minister Gordon Brown said: ''The Labour Party will co-operate fully and in every way with the inquiry. What happened was unacceptable and it is in the public interest that every question is answered.''