On Expenses, BBC Four

Speaker Michael Martin, Labour MP for Glasgow Springburn, was presented as an antediluvian relic of the worst of Old Labour, dredged up from a bottomless well of class resentment and ingrained bigotry. Normal Commons practice would have put a Tory Speaker in to replace the departing Betty Boothroyd, but Martin (played with a deliciously sly touch by Brian Cox) cannily tapped into Labour's primordial mythology to upset the form-book. "So we work the tea-rooms, call in a few favours," he instructed his smirking cabal of co-conspirators, which included such shamelessly barnacled old stagers as Alan Keen (Tim Pigott-Smith) and Stuart Bell (David Calder). "We'll get some senior party men behind us - make this tribal."

His pals backed him to the hilt because of his commitment to defend the rights (real or more often imagined) of MPs at all costs, the higher the better in the case of the latter. Martin, once bedecked in his resplendent new plumage, saw it as his right - in fact, his class-driven duty - to avail himself of every perk and privilege the gilded Westminster fruit machine could spew out. His initial chippiness when a plummy-voiced flunkey inquired as to the identity of his tailor ("I don't have a tailor") was swiftly mellowed by the rich torrent of taxpayer-funded largesse which flowed down the corridors and under his door, barely monitored by the supine Fees Office.

But little did MPs realise that nemesis was approaching in the shape of American journalist Heather Brooke (Anna Maxwell Martin), whose tenacity and indignation when confronted with a wall of supercilious official secrecy ought to be an inspiration to us all, but tragically won't be. Brooke, author of a book about the Freedom of Information Act called Your Right To Know, began trying to chisel out details of MPs' expenses in 2004, though it wasn't until 2008 that she won a High Court decision ordering disclosure. MPs nobly responded by trying to table an amendment to the FoI act which would exempt themselves from it.

"What kind of banana republic am I living in here?" shrieked Brooke on hearing this news. "Why aren't people storming Parliament about this?" An eminently valid question, which many of us ask on a daily basis. But it was Brooke's bitter fate to have the rug whipped out from under her by the Daily Telegraph, who received the priceless leak of a complete breakdown of MPs' unexpurgated expenses and duly held the Dishonourable Members' feet to the fire with sadistic thoroughness. "This fucking story belongs to me!" she raged, leafing impotently through page after broadsheet page of blood-boiling revelations.

Chivvied along by Simon Cellan Jones' nimble direction, On Expenses was sharp, droll and provocative. It's impossible for outsiders to comprehend how the "mother of Parliaments" ever managed to sink so low, but the film seemed to think that greed, complacency and stupidity played prominent roles. There was a wonderful moment when Tim Pigott-Smith, playing Alan Keen about 50 watts dimmer than an energy-saving lightbulb, wailed: "This freedom of information stuff actually applies to us as well?"

Interestingly, the piece portrayed Speaker Martin as being more alive to the career-terminating perils of enforced disclosure than many MPs, but his proposals to begin implementing measures for greater transparency were considered intolerable by the Members. "Can't you see what's coming, or are you just too stupid to care?" he demanded. Apparently the answer was (b). We now see the consequences all too clearly, as our once-great ship of state wallows like a rotting prison hulk on the Thames. Not many tears would be shed if it went down with all hands.

• Click for Heather Brooke's web page
• Watch On Expenses on BBC iPlayer