THE deputy First Minister is facing a police probe into a breach of Holyrood expenses guidelines that resulted in him receiving around £50,000 in mortgage payments charged to the taxpayer.

Lothian and Borders police have been asked to investigate why Nicol Stephen, the Scottish Liberal Democrats leader, gave inaccurate information to parliament about a loan he took out on a property in Edinburgh.

Solidarity MSP Tommy Sheridan is also threatening to take the matter to Holyrood's standards committee.

The row follows the Sunday Herald's revelation last week that Stephen, who is also the Scottish Executive enterprise minister, is billing the taxpayer for mortgage interest payments on a house jointly owned with his wife. He has been charging the public almost £9000 a year through the Edinburgh accommodation allowance (EAA) to stay in a house in Morningside, despite rules blocking payments for joint mortgages.

Stephen failed to tell the parliament in 2003 that his mortgage was taken out with his wife and instead submitted a document which only had his name on it, thus entitling him to the payments.

The revelations prompted Stephen to inform officials about the false information he provided just hours after the Sunday Herald story came out.

The parliament's corporate body, which runs Holyrood, ruled on Thursday that Stephen had "failed to follow the guidelines" on allowances and slapped the MSP on the wrist. But Holyrood stopped short of calling on Stephen to pay back the near £50,000, as members ruled he had not intended to break the guidelines.

Stephen accepted his error but claimed he had not benefited financially. The deputy First Minister said he would transfer the property into his name, a move that will entitle him to keep claiming the payments.

However, a member of the public has urged police to investigate the Minister's role in providing false information to the parliament. The letter of complaint calls on officers in Lothian and Borders police to examine whether an "error" was committed and why the LibDem leader declined to inform parliament he had a joint mortgage.

And Tommy Sheridan said: "I am going to write to the presiding officer, George Reid, because I think it is wrong that people who receive the allowance judge whether another member who received the EAA broke the rules. If he doesn't do anything about it I will refer it to the standards committee."

A Scottish Liberal Democrats spokesman said last night: "There is no question of gain to Mr Stephen or his wife and no cost to the parliament. The parliamentary authorities have made it clear that there has been no improper use of allowances."