HOW can MPs have claimed for moats, manure and home loans that did not exist – and yet have done so with the agreement of the House of Commons authorities?

The question goes to the heart of a puzzle behind the expenses scandal, albeit one that offers no excuse to MPs who have abused the system to spend lavishly and dodge taxes.

The answer is that the fees office clearly colluded with MPs in bumping up their expenses claims, rather than acting as a body concerned with protecting taxpayers’ money.

But behind that explanation lies an extraordinary story in which the Commons Fees Office fought to keep these expenses scams secret – spending countless hundreds of thousands of pounds of our money in the process.

It’s time to meet Andrew Walker, who is apparently paid £125,000 a year to run the fees office, yet argued his staff could not possibly scrutinise the details of claims.

Memorably, when fighting the release of expenses’ receipts at a tribunal last year, Mr Walker said: “There might very well be a degree of curiosity that went beyond the necessary public interest.”

He also acknowledged that, prior to 2002, MPs did not even have to submit documents to support claims for mortgage interest – suggesting even worse scandals took place that will never be uncovered.

And, defending the way MPs could claim up to £250 without receipts, Mr Walker added: “Where there are no receipts, there is no checking. If it’s below £250, then the assumption is that it’s going to be reasonable.”

Asked if MPs could claim a large plasma TV on expenses, Mr Walker brushed the suggestion aside, saying: “I am glad to say that story was misconceived.” Now we know many MPs did exactly that.

It went on and on. Arguing “transparency will damage democracy”, he told the tribunal: “What you are doing is preparing a peephole into the private lives of a member, which will distract them.”

So the fees office is partly to blame for the expenses disaster, although that cannot – as I argued earlier – excuse misbehaving MPs.

But who was standing behind Mr Walker, as he fought the inspired journalists trying to uncover the scandal, while the public – and, I’ll admit it, this reporter – remained in blissful ignorance?

Who placed every possible obstacle in the way of that five-year investigation, blocking freedom of information requests and fighting them at both an information tribunal and the High Court?

It was Michael Martin, the departing Speaker, who threw taxpayers’ money at expensive barristers, presumably hoping to scare off the reporters with the threat of bankruptcy.

When his own legal team advised him not to go to the High Court, Mr Martin sacked them and found another more than happy to grab the taxpayers’ booty.

And that is why we should all celebrate the Speaker’s historic departure.

FORGET the moat and the manure, the helipad and the plasmas, the bath plugs and porn movies, and even the dry rot in a home hundreds of miles away. One expenses claim, for me, stands out above all others, if only for its narcissism.

Step forward Chris Huhne, the Liberal Democrat home affairs spokesman, who got the taxpayer to pay £85.35 for a mounted and framed picture – of himself.