Around six and a half million people voted tactically at the 2017 general election, a study released on Monday 21 August has claimed. The Electoral Reform Society's report also revealed that the June poll saw the second highest electoral volatility (the movement of votes between parties) since 1931 because people are shopping around at "astonishing" levels.

"This surge in tactical voting – double the rate of 2015 – meant voters shifted their party allegiances at unprecedented rates, with the second highest level of voter volatility since the inter-war years. A system designed for two parties cannot accommodate these complex electoral swings," said Darren Hughes, the chief executive of the Electoral Reform Society.

The vote, which saw the Conservatives lose their majority of MPs in the House of Commons, exposed the instability of the First Past the Post voting system, the group argued, with 22 million votes (wasted) at the election as just hundreds of voters in marginal seats had the biggest impact on the election result.

"In the nations and regions of the UK, elections now feel more like lottery than a real choice. As we've shown, tiny shifts in the vote result in drastically different outcomes. Having results hinge on a few hundred voters is no way to run a modern democracy," said Hughes.

"The vast majority of votes are going to waste, with millions still stuck in the electoral black hole of winner-takes-all. A diverse and shifting public having to work around a broken two-party system. The result is volatile voting, and random results in the different parts of the UK.

"There are a wide range of systems where votes are not thrown on the electoral scrapheap. We need to move towards a means of electing our MPs where all voices are heard and where people don't feel forced to hold their nose at the ballot box."

A government spokesperson said: "We are pleased the Electoral Commission's report into the 2017 general election found the elections were well run.

"First Past The Post is a voting system that offers a robust method of electing MPs. A referendum on changing the voting system for general elections was held in 2011 and the public voted overwhelmingly in favour of keeping the First Past the Post system. This Government has no plans to change that position."

General Election 2017: demographic analysis