Washington, unlike London, is a one-industry town. It's the Detroit of politics. Spend a couple of hours walkabout and you soon notice the place is constructed around politicians. Boulevards cut through parkland and head towards marble monuments built for such presidential big-hitters as Lincoln and Jefferson. Meanwhile, blocks of public buildings rise up with the names of rather more obscure officials. There's the Rayburn Building, named after Sam Rayburn, Democrat Speaker of the House of Representatives for 17 years. And just across the road is the Hart Building, an epic glass construction in honour of Philip Hart, who served as senator for Michigan for 18 years. If you flew into town, you probably touched down at Ronald Reagan Airport. And we've all heard of him.

Try to imagine how we'd feel if we commemorated British politicians in this way. Could we drive along Tessa Jowell Avenue without smirking? Would we seriously want to display our address if we worked in Nigel Lawson House, or travel if we had to board a train at Francis Maude Central? It wouldn't work, because we don't see our politicians as part of our public heritage.

The US president is head of state, commander-in-chief and first citizen. In the UK, our head of state is the Queen, and our senior politicians are officially servants of her and her people. There are no qualms about degrading the office of prime minister. When we're done with its occupant, the morning after an election defeat, he or she is duly dumped out the front door, while their belongings get packed and driven off into oblivion in a removal van.

This distinction was in my mind when I was planning Veep, my comedy set in the office of the US vice president. My Westminster comedy The Thick of It is located in a Whitehall hothouse where cabinet ministers know they're fair and constant game for the media and for their opponents, whether within or outside their own party. But Veep could never be a simple translation of that set-up; there could be no Malcolm Tucker figure shouting at, insulting and bullying the vice president as he does in The Thick of It.

If he did, he would immediately be hurled to the ground by five enormous secret service agents, bundled in the back of a high-speed people carrier, driven to Ronald Reagan Airport and flown to somewhere hot, dark and terrible.

That's not to say that the American public doesn't dislike its elected representatives; percentage turnout in US presidential elections is pretty low (usually in the mid to low 50s), while at the moment a record low of only 15 per cent approve of how their Congress is performing. America is very strong on detesting its politicians, even though it steadfastly reveres the office those politicians hold.

The trick is to separate the fallible personality from his or her unassailable office. America has a long tradition of investigative journalists and Capitol Hill representatives who have challenged, threatened, entrapped and censured the hapless individuals who sit in the Oval Office, justifying these attacks on the basis that their target is "demeaning" the office he's been elected to.

It was clear from my research trips to DC that if I wanted the portrayal of the vice president to be accurate, I'd have to show people extremely respectful to her face. But the accuracy would only stand if I also showed how disrespectful they were once she left the room. That's the Washington way: hold the office in high regard, and then dump on the occupant for not maintaining the high standards required of them.

American politics tiptoes across this tense, contradictory landscape. Its politicians can only get elected if they talk in elevated, abstract visions of goodness, hope, futures and change - on the preservation of the American Ideal - but their day-to-day business is conducted in a brutally partisan fashion.

In the UK our main political parties are all coalescing towards a flabby centrist position (so much so it's getting impossible to tell them apart). Parties here don't want to worry us, so they say they're nothing like they were in the past and how moderate they are in the present.

Meantime, in the USA the opposite is happening. Republicans and Democrats campaign on how far the opposite they are to each other, on how much of their opponents' legislation they've blocked, on how completely and utterly their rival is the very last thing America needs right now, and take pride in the extremity of their position.

Democrat and Republican majorities in state legislatures can use their majority to redistrict congressional constituencies so that the new grid favours the party in power. Senators on the minority can still talk out bills that harm their interests. Powerful figures, with wealthy backers, can change state law to make it harder for opponents' supporters to register to vote.

This aggressive in-fighting even goes as far as the Supreme Court. The court is meant to be America's moral and dispassionate high ground, but it's peopled by judges appointed by presidents for their fail-safe adherence to a liberal or conservative perspective on the law. At the moment, it's 5-4 to the conservatives.

That's the fascinating - and worrying - thing about US politics. A constitution is revered, but also applied in an unashamedly partisan way for individual rather than common ends. The people vote politicians into power, and politicians can use that power to frustrate the people.

The first episode of Armando Iannucci's new comedy Veep airs tonight on Sky Atlantic at 10:00pm