806,116 votes in Wales counted for nothing because of the First Past the Post system of electing MPs, the Electoral Reform Society said.
52.2% of votes cast in Wales did not go towards the MP chosen by electors to represent the seat.
Ynys Môn was one of the seats won with the smallest share of the vote. 64.5% of electors voted for a candidate other than the Conservative who won the seat.
Only four seats in the UK were won with a smaller share of the vote than Ynys Môn. The Electoral Reform Society is calling for a more proportional system.
Senedd elections in Wales already use a proportional representation system where the number of members selected is much closer to their share of the vote.
The ERS also highlighted ‘warped’ results. The Conservatives’ share of the vote only went up 2.5% in Wales but their share of the seats went up 15%.
Darren Hughes, Chief Executive of the Electoral Reform Society, said that First Past the Post had left millions of voters “totally unrepresented”.
“These warped results are hard-wired into Westminster’s winner-takes-all voting system,” he said.
“It’s a stark reality that the majority of people did not vote for their MP. Westminster’s electoral system is not just bust, it is bankrupt. First Past the Post politics has driven a coach and horses through attempts at dialogue, compromise and cooperation.
“We can’t go on like this. It’s time for Westminster to catch up with most developed democracies and back a genuinely fair, democratic politics – where seats match votes and all voters are heard.
“First Past the Post is forcing people to ‘hold their nose’ every election. It is reducing choice through back-door party pacts. And it is leaving voters alienated and excluded, while warping our national debate.
“We urge all parties to put principle first and bring our political system into the 21st century. With trust in our institutions at rock bottom, this is a vital first step to building a better politics.”