Nearly 15 years ago I found myself in a small office digging through boxes of receipts looking at the expense claims of local politicians. Everything was laid bare: all the trips, all the meals, all the hotel bills, all the contracts. I was a young trainee reporter covering the Washington State government, and my editor had suggested I look at these claims to see if there were any instances of corruption or personal enrichment.

The laws of the state required that all expense claims and receipts be open to the public. And do you know what I found? Nothing. Not one instance of an improper claim or misuse of money. That is the result of transparent government.

Fast forward to 2004 and I find myself in London. I decide to replicate the exercise in the Mother of Parliaments. I ask the House of Commons for a detailed breakdown of MPs' expenses. So unusual is this request that the officials greet my question with stunned silence. The public aren't even allowed in the Commons Library to access official documents paid for with public money, so there's no way they're getting anywhere near expense records.

Later, the officials tell me they're publishing annual bulk figures. But that's no good, I tell them. A myriad of sins can be hidden in bulk totals. An MP can claim £23,000 for a second home but there's no way to see if it is a legitimate expense without a detailed breakdown. Is it for mortgage payments or a new kitchen? Food or a new flat-screen TV?

When the Freedom of Information Act came into force in 2005 I used it to ask for a detailed breakdown of MPs' travel expenses, staff allowances and finally their second-homes allowance. I encountered relentless opposition from the Commons authorities and Michael Martin, the Speaker. Andrew Walker, the House of Commons' director of finance and administration, said with a straight face that he believed the transparency I sought was bad for democracy. He thought it mere “public curiosity” rather than “public interest” and that it would impinge on MPs' jobs to have to account to the public.

Finally, this week, my three-year battle culminated with the Information Tribunal ruling that MPs must disclose all documentation associated with their second-homes claims. But many MPs are angry about this. They think it's an invasion of their privacy and that my campaign is some sort of witch-hunt. They just don't get it. In a democracy MPs are supposed to be directly accountable to the people they represent; not accountable to other politicians, or officialdom, but to us.

As I listened to Mr Walker testify, the scale of parliamentary arrogance became clear. He didn't even try to hide the fact that there were little or no checks on MPs expense claims. Why should there be? They are honourable members. I could just imagine Mr Walker as Lady Bracknell. The public? As though the very idea of an MP being accountable to the public was so beyond the pale it could barely be allowed in polite conversation.

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