Many years ago, when I was a hack in the Westminster lobby, a newly-elected woman MP came up to tell me of her surprise when, on her first day in parliament, she was taken aside by Michael Martin and friends and shown how to fill in her expenses. Had to get the priorities right, after all. Some things are too important to be left to chance.

She went on to become a minister, he became Speaker of the House of Commons, but for all the grandeur of his surroundings, Michael Martin always remained essentially a shop steward - a guardian of the pay and conditions for the amalgamated union of MPs and allied trades. He's a kind of parliamentary Red Robbo. And that is why many MPs stood by him and do so today - out of fear and affection - as the clamour rises for him to step down from the Speaker's chair because of liberal use of expenses.

He is also Clyde-built and does not like hacks like me poking their snooty noses into MPs' business. After a comic-opera altercation in the members lobby in Westminster, about a piece I had written about how MPs harvested their expenses, Martin once reported me to the Deputy Serjeant-at-Arms. He didn't chop my head off, but it was a close-run thing. Nowadays, Martin has the top-drawer libel lawyers, Carter-Ruck, employed at public expense to defend his image. So let me say right away that Mr Speaker is a man of impeccable integrity, a teetotaler, who, I'm sure, has never fiddled his expenses.

But you have to look at the current expenses row from Martin's trade union mindset. To him, a job's a job, all jobs have perks associated with them, and there's no reason why MPs should be any different. So long as they are obeying the rules, it is nobody's business but theirs.

So, he has claimed £75,000 in accommodation allowances for a house he already owns without a mortgage. That is within rules, and lots of other MPs do exactly the same. So, he charges parliament £7595 for using a room in his house as a constituency office, even though his house isn't actually in his constituency. Again, fully declared and passed by the Parliamentary Fees Office. His wife used taxis to go shopping, but how many business executives can say they have never used taxis for personal use? He has used air miles for family trips? Oh, come on Now, I don't have a lot of sympathy for Michael Martin, who has not been a great Speaker and, after nearly eight years, has overstayed his welcome in the Commons. He has also been an obstacle to the reform of parliament and the introduction of freedom of information to Westminster. However, I can understand - well, sort of - why he might be indignant at being painted a sleazeball for sticking to the rules. But times change, and Speaker Martin hasn't changed with them. We are living in a period in which the Palace of Westminster is being dragged kicking and screaming into the new era of transparency and accountability, which this Labour government itself initiated following the sleaze scandals of the 1990s. As with the dodgy donations row, which brought politicians such as Wendy Alexander to the brink of resignation, Labour politicians never thought that the new strictures really applied to them. Now they know.

Actually, a lot of Speaker Martin's problems really began in Holyrood. It was the Scottish Parliament that introduced proper financial accountability to British politics. It's no accident that the kind of troubles with which he is now afflicted are instantly recognisable to anyone who has been following our petty scandals.

David McLetchie, the Scottish Tory leader, had to resign over his use of taxis; Henry McLeish over subletting his constituency offices. There has been a long-running Holyrood row over MSPs such as LibDem Tavish Scott allegedly profiteering on second homes bought with their parliamentary allowances (a row that received a bizarre twist with the Sunday Herald's revelations about the Deputy Presiding Officer, Trish Godman, buying her imprisoned son's flat in Holyrood).

MSPs in the Scottish Parliament have learned the hard way that, in modern politics, you really do have to be "whiter than white", as Tony Blair famously put it. Just sticking to the letter of the rules isn't enough. You have to ask what ordinary voters would make of the rules you play by. Is it right for MPs to use tens of thousands of pounds of public money to invest in the property market? Well, no, it isn't, when so many young families can't afford a first home, let alone a second.

Is it acceptable to employ wives and relatives as researchers and secretaries? Well, the jury is still out on this one, but the Derek Conway affair demonstrated that this practice - which would not be allowed in the US Congress - is no longer safe, and that MPs have to be very, very careful to ensure that the beneficiaries of their nepotism actually do the work.

I find the scandal of Mrs Martin's taxi use - the cause of Mr Speaker's latest crisis - more sad than bad. On Saturday, Speaker Martin's spin-doctor, Mike Grannatt, resigned because he had unwittingly misled the press about the nature of Mrs Martin's shopping expeditions. He had been told - and had, in turn, told journalists - that these were on Palace business and that an official was always with her. Turned out that the "official" was actually the Martins' housekeeper.

It is commendable that the Speaker's wife is so down-to-earth that she takes her cleaner as a companion. It probably never occurred to her, or her husband, that she was doing anything wrong. Indeed, she probably wasn't, because there is nothing in the rules that specifically precludes the use of taxis by the Speaker's spouse. But there is now - and the departure of the spin-doctor must surely be the beginning of the end for Brother Martin.

There has been a deal of snobbishness in the way that certain Tory columnists have ridiculed Martin because of his accent and his Scottishness.

There is a class issue here. But by his personal conduct, and by his unwillingness to make MPs open and transparent about their personal use of public funds, he has shown that he is out of touch and out of time. The days when MPs could hand in expense accounts without receipts is long gone, as are the days when they regarded their parliamentary expenses as part of their salary. It's time for this superannuated shop steward to be bumped up to the Lords - where he will no doubt be canny in looking after their privileges.