Finally the dam has ­broken, and everyone is talking about changing Britain's political system. For decades reformers have been thwarted by Westminster inertia. But the MPs' expenses ­scandal has overturned old certainties and made change possible.

This moment must be seized by all who want a different kind of politics. Warm words, rhetoric and consideration are not enough; indeed, they are a ­guarantee that little will happen. So let us bar the gates of Westminster and stop MPs leaving for their summer holidays until this crisis has been sorted out, and every nook and cranny of our political system has been reformed.

Today I'm setting out a plan of action to get all the changes we need delivered in just 100 days – making it possible for MPs to be sacked by constituents, abolishing the House of Lords, getting corrupt money out of politics and changing the electoral system to give everyone a voice. People will say it isn't possible – parliament can't act that quickly. I say the innate conservatism that marks out our political establishment is part of the problem. Let's stop all this self-congratulatory hype about the mother of parliaments and get on with improving it.

Momentum will ebb away unless we act quickly. Delay would be a victory for those who want to confine change to the bare minimum – the two establishment parties who will talk up reform long enough for the storm to pass, then kick it into the long grass for good.

David Cameron's proposals set out in the Guardian on Tuesday were a masterful example of well-judged rhetoric free of substance and conviction. Open-source software, new select committee chairs and legislative text messages will not rescue British democracy. They are designed, I fear, to provide verbal cover for maintaining the status quo.

Real political change is about taking power from those who have hoarded it for themselves, and distributing it to others. So change will only be ­possible if the vested interests that have ­benefited from the way things are accept that they can no longer ­preside over an institutional stitch-up. For ­generations the Labour and Conservative parties have ­colluded to keep out ­competition. They are like a corporate duopoly, ­setting the rules of the game to maintain ­dominance. And just like in economics, it's ordinary people who suffer: taken for granted, and deprived of the ­ability to make different choices to those imposed upon them.

That is why what Cameron did not say is more revealing than what he did. No mention of the murky business of party funding. No mention of the scandal of an unelected second chamber. The rejection of any change to an electoral system that hands power to governments on a fraction of the vote. Without these changes, British politics will continue to be a game of pass the parcel between two old parties, while the rest of the country switches off,

So instead of long-term consideration of the possibility of tinkering, let us have 100 days of real action: swift, decisive and confident. It really is possible. The details of a reformed system of party funding have already been thrashed out between the parties, months ago. Sir Hayden Phillips secured outline agreement to ban donations of more than £50,000, limit spending to £100m over a parliament and shake up union contributions. The reason it wasn't adopted was because the Conservatives walked out, keen to protect donations from tax exiles such as Lord Ashcroft. But there is no reason not to return to what was all but agreed, and enforce it. The political parties and elections bill, now before parliament, could be amended and adopted within weeks.

Similarly, on House of Lords reform, the principles of a fully elected chamber have already been exhaustively debated and adopted by MPs. As in any bicameral system, peers should be elected on a different constituency basis and electoral cycle to MPs. Details could be decided on and introduced in the constitutional renewal bill being promoted in the House of Lords by Paul Tyler.

And then there's electoral reform. The ideal solution would be an Irish-style single transferable vote system in which voters elect the person, not the party. But even alternative vote plus – as first advocated by Roy Jenkins in 1998 and now backed by Alan Johnson – would ensure most MPs have a personal constituency link with their voters, as already occurs in Germany and Scotland. Labour made a promise more than a decade ago to hold a referendum on the Jenkins proposals. If the government won't call a general election, let us have this referendum in early September, as the culmination of 100 days of reform.

Together, over the next 100 days, we could achieve nothing less than the total reinvention of British politics. These months could become a great moment in British political history, rather than a shabby footnote to a shameful month of scandal. Let us seize, not squander, the opportunity for change.