UK elections: Inside the House of Commons

The House of Commons in London's Westminster is the cockpit of Britain's democracy and this year is the 850th anniversary of its creation. It has sentenced a king to death, witnessed the assignation of a prime minister and declared wars across the globe. With its famous clock tower that houses Big Ben, what's often called the mother of parliaments is probably the most iconic architectural image in the world.

But very few people know what MPs really do inside the Commons. Once you enter, you see stern signs everywhere saying photography is strictly forbidden. And the Commons authorities have always resolutely set their face against allowing documentary cameras inside to film what happens behind the familiar facade. Until now, that is.

Two years ago for the first time - and five years after I had initially approached them - the Parliament's top people relented. They gave me permission to film an observational four-part documentary series now being screened on BBC World News, about the Commons and the people who work there - with unrestricted access to all areas. 

The stars of the show are the MPs themselves - from the prime minister downwards - along with the hidden armies of parliamentary officials, legal experts who still wear 18th century clothes, skilled craftsmen and other manual workers. They share top billing with the Palace of Westminster itself - a weird and wonderful building that was rebuilt at the height of Britain's Imperial power after it had burnt down in 1834.

With a hundred staircases, over a thousand rooms, three-mile maze of passages, and seventeen restaurants and bars, it's often referred to as the Westminster Village - and it has ten thousand pass holders. Prime Minister David Cameron told me: "You do feel a real sense of history in this place. It's half like a museum, half like a church, half like a school."

Clearly an unusual school where three halves make a whole. Many MPs call the Commons Hogwarts, the school of wizardry in the Harry Potter novels. MPs often find themselves walking down a passageway in the Commons that leads to absolutely nowhere. There are 650 MPs who come in all shapes, sizes and ages. Our series follow the stories of a number of them as they seek to weave their ways through the Commons labyrinth. Some are old hands and some new. And all of them admit to occasionally getting lost in the place. Sir Nicholas Soames, Churchill's grandson, tells me: "I found somewhere the other day I never even knew existed, and I've been here 30 years. It was a bar."

The one part of the Commons where cameras have been allowed since 1989 is the Chamber. But the cameras are under the control of the Commons authorities and coverage of debates is strictly controlled. No one has until now been allowed to film on the floor of the House with no restrictions. We were able to see the whites of the eyes of MPs as they debated, rather than the tops of the heads that the fixed unmanned official cameras capture. 

The Commons chamber is built for direct confrontation with government and opposition benches facing each other. The week's highlight is the half-hour session of questions from MPs to the prime minister, with the opposition leader guaranteed to ask six questions. The Labour Leader Ed Miliband told me: "the noise can be deafening: there are not many jobs where you go to work and have at least three hundred people trying to shout you down".

Prime ministers are not at all keen on the weekly session. Tony Blair said: "It's a nerve racking, discombobulating, nail-biting, bowel-moving, terror-inspiring, courage-draining experience." In his Commons room, David Cameron nodded animatedly when I put Blair's quote to him. "There isn't a Wednesday", said Cameron, "that you don't feel total fear and trepidation about what is about to happen. I'm normally sitting here preparing for PMQs and about five minutes beforehand you think 'oh no, have I got to do this again?'"

Our series also deals with the biggest immediate question facing MPs and the Commons authorities: the state of the building itself. John Bercow MP, the Commons Speaker, says: 'We've got mice crawling around, we've got huge plates of glass falling down, we had effluent coming into one part of the building."

And we filmed leaking roofs and buckets to catch the drips. We saw paintwork peeling, plaster and stonework crumbling. And Big Ben itself is starting to lean. The place costs a fortune to maintain, and it's estimated that the bill to repair and renew will cost some three billion pounds. 

There are some MPs, notably the more recent ones, who feel that this would be the time to take the momentous decision to move from the Palace of Westminster and into a purpose-built 21st century legislature. The Labour MP Sarah Champion says: "to me the Commons is just a high Victorian pastiche of power. I'd have it for weddings, conferences and a museum, and have something representative of who we are now, with really good architecture." It's a suggestion that horrifies David Cameron: "When people say rebuild it, have a semi-circular Chamber, I would hate that. I like the House of Commons looking like it does and I think the sense of history and the connection with the past is very important."

Michael Cockerell is the presenter and producer of Inside the Commons currently being screened on BBC World News this weekend - Saturday at 2.40pm and Sunday at 7.40am and 8.40pm as part of the channel's coverage of the UK General Election. Visit www.bbc.com/ukelection.