The disgraced Tory MP Derek Conway was under fresh pressure last night after Sir Ian Blair, the Metropolitan Police Commissioner, demanded to know why his case has not been referred to the force.
Sir Ian, the country's most senior police officer, has written to the parliamentary standards watchdog John Lyon to ask why detectives have not been asked to investigate after Mr Conway was suspended from the Commons for employing his son Freddie as a researcher paid for from public funds while he was a full-time student.
In a highly unusual move which will pile fresh pressure on Mr Conway, a Metropolitan Police spokeswoman confirmed Sir Ian had written to Mr Lyon and asked for an explanation if the case is not to be referred.
Sir Ian told members of the Metropolitan Police Authority: "There is a protocol. The protocol was agreed with the previous parliamentary standards commissioner. It doesn't appear from the face of it that it was fully followed in this particular case." He added: "What we have done is to write to the standards commissioner and ask him whether he is going to refer the matter to the MPS [Metropolitan Police Service] and if he isn't what are his reasons and we await that answer."
The commissioner went on: "The MPS can – and has demonstrably – investigated matters wherever they arise. But we obviously, and as in the Electoral Commission or in the benefits department or wherever else, start with the position that the adjudicating authority has a right and role first and we will wait and see what the answer is.
"We are just trying to follow the process but we haven't, and we are not, ignoring the situation."
Mr Conway has been ordered to repay £13,161 of the money paid to his son Freddie after an inquiry found no evidence that he had carried out research work. The Old Bexley and Sidcup MP was forced to announce that he would stand down at the next election and stripped of his place on a panel of MPs charged with chairing parliamentary proceedings,
The case has sparked a full-scale review of MPs' allowances and expenses and led to calls for members to publish full details of relatives they employ.
Sir George Young, chairman of the Commons Standards and Privileges Committee, told the Commons last month that the police would not be called in.
A spokesman for the Parliamentary Commissioner for Standards said the position had not changed.
Yesterday the Standards and Privileges Committee recommended that all MPs be required to publish details of family members they employ. Spouses, children, parents and grandparents should be declared to Parliament along with unmarried partners, nieces and nephews and other relatives, the committee said.
They said changes should be introduced from April, but acknowledged that new reporting requirements could be voluntary until a committee of senior MPs reports on wider reform of allowances in the summer.
However, they stopped short of demanding that MPs reveal how much they pay their relatives, saying it was sufficient to give details of their job titles. The committee said there was "a strong case for greater disclosure" by MPs and said several members had already tried to register details of their family on the register of interests.
The committee's report attempted to end the political battle over reform of parliamentary allowances, arguing that reform "is best introduced by the house, rather than through individual initiatives".
David Cameron has ordered his front bench to release details of family members they employ by the end of the month.