Too early to guess the other winners in next year's Academy awards, but if there were a prize for best drama there would surely be no contest. The US election battle of 2008 has been a gripping saga since the first days of January, and it has a global audience hooked. In the last 48 hours, we've had Barack Obama promising that the Republicans can be as tough as they like on him: "I'm going to be just as tough on them." (Message: There Will Be Blood.) Democrats have been hissing at the return of arch-villain, splitter and perennial election-spoiler Ralph Nader, whose 97,421 Florida votes in 2000 helped deprive Al Gore of the presidency and hand it to George Bush.

Nader is 74 and the Republican's presumptive nominee John McCain turns 72 in August - disproving the notion that the US is No Country for Old Men. Oh, and if the Academy is looking for an early nod in the best costume design category, they'll surely want to recognise the Hillary Clinton campaign for Monday's distribution of a photograph of Obama dressed as a Somali elder, complete with turban, during a 2006 trip to Africa. (There was a time when the Clinton team's efforts to marginalise Obama as the black candidate were subtle, but the mood is more desperate now.)

No group is watching all this with more fascination than the villagers of Westminster, some of whose nerdier residents are able to discuss, say, the delegate allocation system in Texas with the expertise of a native. The excitement is so great, they want a piece of it.

Just look at the contrast, they say enviously. The Americans have Obamamania, a politician packing out sports arenas with crowds of 20,000, many of them young and exhibiting an intensity so great it's prompted warnings of a cult of personality. Compare that with a British landscape pockmarked by apathy and disengagement. Incredibly, voter turnout in UK elections plunged by 18 percentage points in just a decade, falling from 78% in 1992 to 59.2% in 2001. Factor in all those non-voters and you see that the current Labour government was the choice of a mere 21.6% of Britain's eligible voters.

Both those facts are highlighted in a crisp, lively pamphlet published this week by the famously independent Labour MP Frank Field. Dedicated to showing how British democracy might be brought "back from life support", the paper has Field as the latest to be looking greenly across the Atlantic.

One of his proposed remedies is to replicate the American mechanism of the party primary, the very process currently catalysing such drama Stateside. To be fair to Field, this is no faddish whim: he has long believed that safe parliamentary seats especially, where the real contest is in choosing the candidate for the dominant local party, should throw open their selection processes. He offers his own Birkenhead constituency, now the 15th safest in England, as a potential testbed for the idea. He imagines everybody in Birkenhead having a vote in choosing the Labour candidate, thereby forcing politicians to appeal beyond the narrow caucus of party activists. An Obama figure could storm in, build a movement, and steal Field's seat from under him. You can even imagine the stirring rhetoric: "Can we change the metropolitan borough of Wirral? Yes, we can!"

I can see the appeal of the primary idea. Indeed, I would be delighted to see it extended to the job that matters most: party leader. Imagine how much more solid a mandate Gordon Brown would rest on now if he had had to win the votes of declared Labour voters in successive contests, first in wintry, rural Lincolnshire, then in tiny Rutland before a Super Thursday of contests in sunny Cornwall, delegate-rich London and pivotal Yorkshire.

Field has plenty of other enticing ideas, too. He wants to have a "none of the above" option on the ballot paper, so voters can express their frustration with the lack of choice, and suggests pressing governments to decide whether a new law is really necessary by obliging them to take off the statute book as many pages as they want to add. He also recommends the French practice of requiring every MP to win more than 50% of the vote in the constituency they represent. Fail to get that at the first attempt, and there would be a run-off contest between the two top-placed candidates a week after election day.

The trouble with all this is that it soon collapses into what Field himself castigates as "the magpie approach to reform", picking up one bright idea here and another there. He tries to anchor his thesis in a broader argument - the need to make government more representative and more responsible - but it still looks a lot like cherry-picking. To paraphrase Mel Brooks, Field wants a little piece of America, a little piece of France.

But this is a bit of a cheat. In the US case, if primaries work, they work not in isolation but because they are embedded in a radically different approach to political parties, and even to democracy and sovereignty. We can't scrape off the tasty icing of primaries unless we're prepared to import the entire democratic cake.

The best example is in Field's laudable call for select committees of MPs to have sharper teeth and stronger bite. He offers several steps towards that outcome - chairmanships to be decided on by a free vote of MPs, committees to have the right to introduce their own bills - which are all perfectly sensible. But they duck the fundamental question, the one that explains why those committees, and parliament itself, start out so weak.

It is because in Britain, unlike the US and France, we do not have a meaningful separation of powers. In Washington, the executive sits in one place, the White House, while lawmakers - Congress - sit somewhere else. Neither depend on the other; each is elected separately and with its own mandate. The result is that the legislature can challenge the executive, exposing it to serious scrutiny and introducing whatever bills it likes.

In Britain, we like to speak about separation of powers but it's a fiction. The government, which increasingly means the prime minister, dominates the law-making chamber where, by definition, it - he - has a majority. The result is a set of committees that may resemble their congressional counterparts but which are nothing of the sort. Here all committees always carry a government majority; chairs are appointed by the prime minister via the whips' office and are even paid an extra £20,000 a year; if they're loyal, they may be rewarded with a government job. If the committees hold the executive to account, as some undoubtedly do, it is despite themselves.

So we can exhort these panels to be more independent, but even a free vote of MPs won't achieve it - not while the governing party has a permanent majority in the Commons. The only solution would be a clear separation of powers - and in Britain that would entail a political earthquake. Either we would have a directly elected PM, admitting the presidential nature of our current system and letting the Commons act as a check on Downing Street. Or we could fully elect the second chamber, at a time other than the general election, and ensure it acts like a separate legislature, holding the executive to account.

Whatever we do, it'll mean more than picking up the glamorous habits of foreign countries. It would require us to be brave and radical - but the prize awaiting us would be far better than any Oscar.