Harrow East MP Tony McNulty has been accused of claiming £60,000 expenses on a Wealdstone home he reputedly does not live in.
Under House of Commons rules Mr McNulty - a Labour politician and minister for employment and minister for London - is entitled to use public money to help pay the mortgage on the second house which he owns.
However reports published this weekend claim Mr McNulty's parents live in the second house - they are certaintly listed on the electoral register there along with him - while Mr McNulty himself lives with his wife in Hammersmith, west London.
Mr McNulty's office this morning declined to comment on the allegations.
Bob Blackman, Conservative parliamentary candidate for Harrow East, said: "I have to say that it appears from what has been said that he abided by the rules. However, that just shows you what is wrong with rules.
"He's making a legitimate claim but it's not within the spirit of the rules. I think he should pay the money back on the basis that he hasn't been living there [at his parents' house].
"My own view is that the whole MP expenses system needs to be thoroughly reviewed."
