By Alex Stevenson

Britain’s three-party politics means the current voting system is less likely to deliver stable single-party governments in the future, a thinktank has claimed.

A report from the Institute for Public Policy Research (IPPR) published today has argued that the first-past-the-post method lets voters down because it cannot be relied on to deliver a clear-cut result.

At the 2010 general election over a third of voters backed parties other than Labour or the Conservatives, handing the two largest parties their worst share of the vote – 65.1% – since the 1950s.

“Britain now has a broken voting system that needs to be fixed,” IPPR director Nick Pearce said.

“Unless first-past-the-post is reformed the UK, will be left with a voting system that neither delivers fair representation nor single party government.”

Mr Pearce argued the last election result was not especially unusual. With parties other than Labour or the Conservatives now requiring an average advantage over each other of at least 86 seats to secure an overall majority, hung parliaments become much more likely.

“Britain has evolved into a multi-party system, but it still has an electoral system designed for only two parties,” Mr Pearce added.

With the referendum on changing to the alternative vote system coming in May arguments about the respective merits of the two forms will only intensify in the coming months.

Opponents of first-past-the-post will be able to use much of today’s report to their advantage. It showed that the 2010 general election was decided in just 108 marginal constituencies – by fewer than 1.8% of the electorate.