The voting system is so broken that the Brexit Party, Lib Dems and Plaid Cymru are joining forces to replace it

But the process has to be deliberative. Just like Ireland created citizens' assemblies to break the deadlock over reproductive rights, so must we involve the public in changing our staid electoral system

Today marks the launch of a new cross-party agreement on electoral reform, of which Plaid Cymru is a founding signatory.

I join a broad array of political parties – the Lib Dems, the Green Party, the SNP, the Brexit Party – and MPs from across the spectrum in signing the “Good Systems Agreement” brokered by campaign group Make Votes Matter. This is the first time such an agreement has ever been made in the UK.

There is little that such a list of parties all have in common with one another, but we all share the belief that the First Past the Post system cannot adequately represent a diverse, modern electorate – nor can we rely upon it to deliver responsible, representative government.

The agreement sets out the principles that we believe a new voting system should deliver. Some of these are fundamentally incompatible with the archaic First Past the Post system used for Westminster elections. For example, we believe that seats in the House of Commons should match the votes cast in a general election.

Under the current system, a smaller party can win a significant number of votes, but still end up with no MPs if they fail to have a high enough concentration of votes in any one constituency. This system is designed for a two-party political system that has outlived its usefulness for modern politics.

Our current system delivers results like those of 2015, when two parties winning millions of votes ended up with just two MPs between them. Parliament is supposed to represent the whole electorate, but there are many who will not feel represented until seats match votes.

Similarly, we believe votes should be equal in value, without the distortions we currently see based on where you live and who you vote for. When an election comes, parties are compelled to throw everything at the handful of marginal constituencies to the detriment of the majority who live in safer seats. This cannot be right. Votes should count equally, wherever they are cast and whoever they are cast for.

But there are features of our current system that we all value. The important constituency link between MPs and the communities we represent must remain. And we must keep the practice of voting for named candidates, not just for parties. Fortunately, different systems are already in use in the devolved parliaments – and further afield – which deliver on all these features.

Now, more than ever, we need a roadmap to changing the voting system.

An expert panel’s recent review of the voting system used for elections to the National Assembly for Wales showed there is potential in putting the question to an independent body. The panel took their work seriously and made sensible recommendations to the Llywydd (the Presiding Officer) for how to improve Welsh democracy.

But it also showed the limitations of such an approach. A lack of citizens’ involvement in the decision-making meant there was little sense of public ownership over the proposed change, and little to stop the issue being kicked into the long grass.

Instead, we need a citizen-led process to recommend a new voting system for our general elections. A citizens’ assembly is a large group of ordinary people selected rather like a jury, but with care taken to ensure it is representative of the population at large.

With the opportunity to hear from and cross-examine experts, such bodies have been able to understand, deliberate and find the best solution to even the most challenging issues. If such an approach can break the deadlock over reproductive rights in Ireland, I have no doubt it can choose a voting system that puts voters in control of Westminster.

When I met Professor David Farrell recently, who was the research director of the Constitutional Convention and the research leader of the Citizens’ Assembly, he was keen to stress that the momentum behind citizens’ assemblies in Ireland was in large part driven by the deep economic crisis that brought the political system to its knees following the 2008 financial crisis.

Surely, we as politicians must accept that we have reached a political crisis of comparable magnitude and that we must therefore consider alternative solutions.

With so many people feeling let down by the traditional two main parties, it looks like the next general election could test First Past the Post like never before.

When people vote for diverse parties under a system designed for just two, the results are unpredictable, perhaps even dangerous. Certain parties will be arbitrarily punished, others hugely over-empowered. The views of voters are relegated to a footnote.

It is incumbent on democrats to fight for a fair system rather than merely hoping it is they who will hit the jackpot, particularly given how much is at stake in today’s politics.

Liz Saville Roberts is the Westminster leader for Plaid Cymru and the MP for Dwyfor Meirionnydd