I have no settled opinion about Caroline Spelman, the Conservative Party chairman. She must have spent her career below (or possibly above) my flickering and faulty political radar . However, while probably scuppering her prospects in Mr Clean-Up Cameron's party, she has unwittingly done the rest of us a favour. By “us” I mean any woman who combines early motherhood with some sort of professional life - partly working from home - and knows what a muddle it is.

You know the story. Ms Spelman has found her maternal flank exposed in the middle of an unprecedented season of revelations about MPs and MEPs milking the taxpayer of expenses for their second home “needs”, and then bleating that they stayed “within the rules”. Rules that they make, and tried hard to keep secret. This overdue parliamentary witch-hunt has been grand sport for onlookers: the discomfiture of stout felines in Parliament is consoling to the rest of us at a time when living costs are rising fast, taxes are high and the Revenue more nitpickingly spiteful than ever before towards the self-employed. The only regret is that while a couple of the more outrageous milkers of expenses have been sacked or demoted, most of them sail on undamaged, “within the rules”.

Not within natural justice or reasonableness: just the rules. Here is Barbara Follett, millionaire's wife, charging you and me £94 every three weeks for window-cleaning; meanwhile, Margaret Beckett's garden cost us £6,500, including rockery (so important for a minister to have a good rockery, don't you think?). Here are Ann and Alan Keen netting £100,000 of public funds by having a mortgage each, and Ed Balls and Yvette Cooper also doing rather well from his 'n' hers claims. Oh, and marvel at Peter Mandelson's new shower, for which we paid £3,000 five years ago (the ritziest shower in Hartlepool, I'll be bound).

And Tony Blair? Don't start me. Not only did his new Trimdon kitchen cost us £10,600 (plus £50 for servicing the Aga), but thanks to the fine ferrets who battled for disclosure we can now gaze, online, at the very forms on which a Prime Minister made us pay the mortgage interest on £90,000. He borrowed it against a house which - Mrs Blair writes - only cost them £30,000, plus the same again to do it up. Is that a legitimate expense? Did Blair need to spend that money in order to have a billet in his constituency? No. It was bunce. The loan - whose interest we paid - went to fund his future property in Connaught Square.

It was “within the rules”. Just as Honourable Members - who have hobbled employers with strict anti-discrimination law - can pay public salaries to their family members without any open interviews to see if there are better candidates; just as the ridiculous “John Lewis List” lets them charge the taxpayer £150 per dining chair, demand free dry-cleaning for their personal clothes, and spend £795 of our money on a sideboard and £750 on a stereo (God forbid they might have to go to Currys). They may charge a grand total of £23,000 of home equipment, to keep for ever, untaxed. As for MEPs, draw a veil. It's Monday. Nobody feels strong enough to think about that.

This degrading and ridiculous gravy train chugs on, within the dear old rules. But what is this dreadful deed that Caroline Spelman committed?

Eleven years ago, with three young children, she hired a young woman to mind the children after school and nursery and also to help with the post and phone calls which beset an MP. Tina Haynes was a trained nanny, but it is claimed (by Spelman and Haynes alike) that in a home that genuinely doubled as the constituency office, she answered calls and opened and filed the mail once the cereal-soaked chaos of a family morning had subsided.

Cue outrage. “Spelman was stealing from the taxpayers!” cry male bloggers and commentators. The MP explains that the money she paid Haynes was supposed to be for the admin work, while the board and lodging and car rewarded her childcare. Hmm. The Chief Whip didn't like it and blew the whistle, and she stopped. Ten years ago.

It seems clear enough that during that year Ms Spelman was operating beyond the edge of the rules (she would have done better to build a rockery, or take out an unnecessary mortgage to put down a deposit on a mansion). Unfortunately for her, she made the claim in order to pay the young woman who made her working life possible.

Spittingly hateful voices online have been jeering that she “can't prove” the hours her nanny spent as a secretary, especially as one child was of preschool age and there is no proof of his nursery hours. Possibly it does not occur to them that there may have been days when the said child had a cold and wanted his mother, and the nanny came in handy to take over answering the phone and sorting the post and writing things in the diary.

Life in early motherhood is complicated, messy and full of compromise. I can't defend rule-breaking, but it leaves a nasty taste when natural justice and rules conflict. As a voter, though, I know what I want from my MP. If the price of a good, attentive one was subsidising a bit of childcare, I'd not mind much. If the price was ritzy hi-fi equipment and funding a grand retirement pad, I would.

Mothers get hammered whatever they do. Consider the more universal matter of tax-offsetting. Here, remember, individuals do not claim the whole cost but only relief of the 20 or 40 per cent tax on that bit of income.

It is an old injustice, and old feminist carp: why should a tycoon glide round to see his mistress in a chauffered car and deem it a business expense, while a tycooness - contributing equally to the economy - can't claim for the person who makes it possible for her to step outside the house without a baby buggy? Why must a single mother, seeking to better herself and join the taxpaying classes, fund her childminder out of taxed income while her employer claims as corporate-entertainment the cost of taking his old mates to Henley or Spearmint Rhino?

However much the nation pretends it wants their skills, working mothers are still the bottom of the heap. The deep irony this time is that while Caroline Spelman probably did break the rules and will suffer for it, a legion of craftier and greedier servants of the people stayed within them and skip away scot-free. Which is the straighter sort of guy, do you think?

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