It would be the most radical change of all, in this election in which "change" is the buzzword. It would bring Britain into line with the rest of Europe, at long last. It may be about to happen. Yet it's creeping up on us, hardly noticed in the country at large.
Britain may be about to get its first Green MP. Thirty years after the German Greens, Die Grünen, brought about the biggest real shift in post-war European politics by putting the environment on the political agenda for the first time alongside the economy, health and education, the UK may be about to play catch-up, and let a whiff of radicalism into the corridors of power.
In Brighton Pavilion, the most raffish constituency in that most raffish of seaside resorts, Caroline Lucas, leader of the Green Party of England and Wales, is the bookies' odds-on favourite to be elected to Parliament on 6 May. If she succeeds, she will end the remarkable anomaly by which Britain remains the only major country in Europe which has never had Green MPs in its national legislature.
Yet her election would do far more than that. It would be a breach in the wall of Westminster, through which genuinely alternative policies might flow. Nick Clegg has had formidable success in painting himself as the "alternative" candidate to the two "conventional" parties and their leaders, but, as a glance at their manifesto shows, Caroline Lucas and her party, whether you approve of them or not, are offering the truly radical choice. Compared to the Greens, Nick Clegg's yellow-rosetted Lib Dems are every bit as conventional as the party of red and the party of blue.
The Greens have offered that radical choice before, of course. The difference is that the offer may this time be taken up. For Caroline Lucas's major achievement has been to make the Green party electable, or at least, to stop it from being a political joke.
In 1989 the Greens reached a highpoint of political success: they secured 15 per cent of the national vote in the European elections, panicking Margaret Thatcher into ditching her crabby Environment Secretary, Nicholas Ridley, and replacing him with the more sympathetic Chris Patten. Yet their moment was wasted. Despite the efforts of the party's two senior figures, Jonathon Porritt and Sarah Parkin, many grass-roots members resisted the chance to streamline the Greens and make them a party which might win seats at Westminster. They rejected the "cult of leadership", condemning the party to have several figures speaking for it at once, so that its focus was hopelessly split.
Caroline Lucas has changed all that. She led the campaign for the party to have a single leader, and won; then she stood for the leader's post herself, and she won. The former Oxfam adviser is a serious politician, fluent, assured and passionate, with 11 years' experience as the Green MEP for South East England, and she has shaken up both the party's policies and its structures. She has added a major concern for social justice to its ecological roots, and focused its campaigning efforts on the three constituencies where it has a chance of winning: her own, Norwich South, and Lewisham Deptford.
Let's be realistic: in most of Britain, a green vote is not going to get you the MP you want. But in those three constituencies voting Green in 2010 may do so, and even if it were only Caroline Lucas who were elected, the breakthrough, the moment of change in British politics, would be a real one.
To base your political convictions on a concern for the welfare of the Earth is as rational a choice as basing them on a concern for equality, or liberty. That the environment seems to have disappeared as an issue in this election is not a mystery: environmental concern naturally tends to shrink when people are deeply worried about their jobs and their immediate welfare. But environmental problems do not shrink; indeed, they constantly grow. And to send a representative of a party which holds that vision to Westminster as one of our MPs would be quite new.
Thirty years ago, Germany's Die Grünen were sparked into life by a charismatic and radical young woman called Petra Kelly, who led her party into the mainstream of German politics. In 1992, after a debate on the environment in the Oxford Union, I sat in the lounge of Oxford's Randolph Hotel sharing a midnight pot of tea with Petra Kelly, and Sarah Parkin, and Caroline Lucas, then the Greens' young press officer. Petra Kelly talked of her hopes (and her fears) for the future, while her partner, Gert Bastian, sat off to one side, seemingly lost in thought. Three months later, for reasons unkown, he shot her as she slept, then turned his gun upon himself.
Caroline Lucas has come a long way since that midnight pot of tea with Petra Kelly, through years when the her party seemed to many people to be as big a bunch of losers as ever forfeited their deposits, one rung up from the Monster Raving Loonies; yet she has kept faith, and put things right, and if the electors of Brighton Pavilion vote as the bookmakers think they will on 6 May, Britain may have a Petra Kelly of its own.
What a Green victory would mean
"The Green movement seems to me the most rational and honest way of behaving towards the planet we live on, and the Green Party is its political expression."
Philip Pullman, Author
"I think Caroline Lucas will be very exciting if she gets in, because we'll start to see some sway
from somebody who's very well informed and experienced..."
Greta Scacchi, Actress
"The election of our first Green Party MP would put us on the first step of a long journey to safeguard planet Earth for future generations."
Mark Thompson, Astronomer and television presenter
"The correlation between the number of green bottoms on parliamentary seats and the growth of a green economic sector is undeniable."
Sara Parkin, Founder director, Forum for the Future
"They have been able to do what the left hasn't been able to do, which has been to put forward an alternative to the free market and sound credible."
Mark Steel, Comedian
"Vote for what you believe in. There are no real differences between the main three parties. If you really want change, vote Green."
Alistair McGowan, Comedian
"The Green Party is the only political party to have a consistent message on the environment."
Nick Reeves, Executive director, Chartered Institution of Water and Environmental Management
"It is an indictment of our attitude to our own long-term well-being that Greens, who might do us the most good in the long run, have yet to sit down in the Commons."
Simon Woodroffe, Founder, YO! Company
"Wouldn't it be nice to have someone [in the Commons] who is doing more than paying lip service to climate change?"
Thom Yorke, Radiohead frontman, backing Tony Juniper, Green Party candidate for Cambridge
"It is about time a Green Party candidate is elected to Parliament: their focus on the environment is essential to the future of the planet."
Rev Paul Nicolson, Chairman, Zacchaeus 2000 Trust
"The sooner we have a Green MP the better... our world is heating up and we need to have people addressing these issues in Parliament who know what they're talking about."
Kelly Hoppen, Interior designer
"The Greens have remained constant at a 2 per cent voting share recently. This would equate to around 13 seats in the Commons if [we had PR]"
Robert Salvoni, President, Harris Interactive
"I haven't voted Green but I have sympathy with many of their policies... I think there are enough Green voters out there to deserve representation in Parliament."
Frances Crook, Director, Howard League
"The Green Party needs more exposure... It's not a question of having a Green MP, but including green issues and the Green Party in the debate."
Doug Stewart, Founder, Green Energy UK