Leading article: Privacy? Yes. Secrecy? No

"There is a difference between private and secret." So said Ken Livingstone when he told journalists last week – to pre-empt the disclosure by a Sunday newspaper – that he was the father of five children by three women. The Mayor of London is absolutely right, and makes an important distinction that ought to guide our judgement of the standards of conduct in public life.

The Speaker and the Prime Minister tried to use the privacy argument in their doomed attempt to prevent full disclosure of MPs' expenses. Twelve days ago, the House of Commons Commission decided, at the last minute and against its previous legal advice, to appeal against a ruling by the Information Tribunal that details of expenses should be published. That decision – a decision that will cost the public purse thousands in legal fees – was taken at a meeting of the commission called at short notice and attended by two members: Michael Martin, the Speaker, and Harriet Harman, the Leader of the House. It is inconceivable, therefore, that they were acting without the knowledge and approval of Gordon Brown.

It was one of the Prime Minister's poorer judgements, not least because it looks like an attempt to delay the inevitable. More water started to pour over another part of the dyke last week, with the publication of expenses claimed by 11 MPs and one former MP three and five years ago, as a result of separate Freedom of Information requests. Yet the Commons authorities continue their High Court appeal to try to prevent the publication of all expenses at a greater level of detail, item by item.

Initially, their argument against full disclosure was that it would lead to the addresses of MPs' second homes being made public – in other words, information that is private and therefore secret. Unsurprisingly, it is not an argument that survived for long. It would be perfectly possible to publish information about MPs' expenses with the addresses removed. So the argument shifted. The legal grounds for the appeal are that MPs claimed their expenses on the understanding that the information would be confidential. "MPs did not have a reasonable expectation it would be published," claims the document filed by the commission with the High Court.

This is a weak argument. The presumption of Labour's Freedom of Information law is that things should be made public unless there are specific reasons not to do so. It ought to be an elementary principle that elected representatives are accountable to their voters for their use of public money. Yet, at every turn, the House of Commons has given the impression of resisting it – and Mr Brown has shown a depressing lack of leadership. Last May, the month before he became Prime Minister, several allies, including Ed Balls, Nick Brown, Doug Henderson, John McFall and Tom Watson, voted for a Private Member's Bill brought in by David Maclean, the Tory former chief whip, to exempt Parliament from the Freedom of Information Act. This shabby Bill was killed only when it failed to find a single member of the Lords to support it.

Of course, many MPs feel the scrutiny they already attract is intrusive and unfair. It sometimes is. But they would be on stronger ground if they willingly accepted they were publicly accountable for every penny of taxpayers' money they spend – and then invited the media to observe the proper distinctions between the secret, the private and the public.

It is also true that an MP's salary, £62,000, might be modest compared with many professions. But it is not the only factor in attracting high-calibre entrants to the profession of politics: theirs is a calling that offers opportunities for both public service and personal glory. In any case, it would be difficult to secure public support for higher pay – and it is counterproductive, having failed to do so, for MPs to take the money out of the public till when they think the voters are looking the other way.

The time has surely come for MPs to accept the principle of full disclosure. The Derek Conway affair shone a harsh light on an undergrowth of indefensible practices. In what other walk of life could one claim £400 in "expenses" without producing a receipt? When that was exposed to sunlight, the Commons authorities reluctantly cut the figure to £25; but why should any amount be payable without a receipt? To save on administration costs, say the authorities. Sorry, that will not wash any more.

MPs feel their second homes, dishwashers, Sky subscriptions and groceries are private. They are wrong. Ken Livingstone is right. Their children are private – unless they employ them as researchers. Their sexual partners are private – unless they show them favouritism in the public sphere. But what they do with public money is not private, and it should not be secret.