This is an extraordinary political moment. An election seemingly destined to produce a narrow Conservative victory has been seized by the voters and turned into a democratic contest – a contest not just between parties, but over the shape of our democracy itself.

The MPs that assemble in Westminster next month could usher in one of the great reforming parliaments in British history, one to rank in the history books alongside 1831-32, 1865-67 or 1911-1914. The next parliament could see cherished progressive liberal aspirations realised: a proportional electoral system; wider and better-defended civil liberties; a new, internationalist approach to foreign affairs and immigration; reform of the tax system to share wealth and curb carbon emissions; and an assault on the vested interests of the financial sector.

The question for progressive liberals is what election result now offers the best chance of achieving these goals. Certainly not a Conservative majority. Despite some welcome commitments in areas such as civil liberties and localism, the Tories remain instinctively opposed to the deep democratic reforms the country needs.

But a return of a majority Labour government under Gordon Brown would not provide a strong enough guarantee of reform. Labour has a long list of achievements over the last 13 years, of which it can be proud. But Labour has also presided over a ruinous period for civil liberties and has failed to deliver wholesale political reform.

Labour does now promise fixed-term parliaments, an elected House of Lords and a referendum on the alternative vote: too little, too late.

The question is where the energy for the future of progressive politics is to be found. It is a contemporary political fact that the stronger the performance of the Liberal Democrats on 6 May the better the chances of progressive reform.

The Liberal Democrats are today's change-makers. They have already changed the election; next they could drive fundamental change in our political and economic landscape.

Some of us have already pinned our colours to the Liberal Democrat mast. For others, the decision to back the Liberal Democrats in this election is a difficult one. Long-standing party loyalties, even in a less tribal world, are not easily suspended. But May 2010 offers a once-in-a-generation opportunity to reshape politics for the better. It must be seized.

Richard Reeves, John Kampfner, Professor Noreena Hertz, Susie Orbach, Shazia Mirza, Camilla Toulmin, Brian Eno, John le Carré, Henry Porter, Alex Layton, Gordon Roddick, Yasmin Alibhai Brown, Philip Pullman, David Aukin, Nick Harkaway, Lisa Appignanesi, Francis Wheen, Alan Ryan, Raymond Tallis, Julian Baggini, Jeanette Winterson, Rodric Braithwaite, Richard Dawkins, George Monbiot, Ken Macdonald, Philippe Sands, Misha Glenny, Anthony Barnett, Richard Sennett, David Marquand