Fiddling expenses is a crime, as not a few MPs and several peers have discovered. Nor is it just the scale of the fraud that determines the existence of a crime, though it plays a role in setting the penalty. It is the principle: the claiming of money – in these cases, public money – to which someone is not entitled. Now Baroness Warsi, co-chairman of the Conservative Party and the country's first woman Muslim cabinet minister, finds herself in the frame.

The accusations are twofold. First, that she claimed up to £2,000 in expenses for accommodation that, it is agreed, she had been invited to use by a friend. Second, that she broke parliamentary rules by not declaring rent from letting out her London flat. On the second, she has admitted fault, but insists that the oversight was brief, unintentional and soon rectified. On the face of it, this looks like a storm in a teacup. The first accusation is far more serious, both because of its resonance with other expenses cases and because the explanations she has offered appear vague. Clarity must await her return from abroad or, if her account is still judged unsatisfactory, the outcome of an investigation.

While expenses fraud is not something to be trivialised, however, it is hard not to detect a whiff of something untoward behind the targeting of Lady Warsi. The accusations relate to a few weeks in 2008, that is before the MPs' expenses scandal broke, when few questions were asked about peers' allowances. More significantly, perhaps, the owner of the accommodation in question is in dispute with the Conservative Party over recognition of his Conservative Arab Network. There has been more than a hint in his public statements of favours given and perhaps owed.

It should also be noted that there has been no stampede of Conservatives rushing to Lady Warsi's aid. Her relative youth, gender and background are huge assets for David Cameron, giving the Government, and the party, an appearance of inclusiveness it would otherwise lack. But those same features also set her apart from the Westminster rank and file. Some, it would appear, find it hard to treat her as "one of us"; others whisper that she is not up to her job.

Such considerations cannot be ignored as the pressures mount for an investigation. If she is to be condemned, however, it must be because she is found to have acted fraudulently, not because of a witch-hunt started for quite different reasons.