Two by-elections will take place on February 23rd. One in Copeland, West Cumbria, and the other in nearby Stoke-On-Trent. The Labour held seats have become vacant because of the resignations of Jamie Reed and Tristam Hunt for alternative lucrative careers. Apart from political anoraks, most by-elections arouse little interest amongst those eligible to vote. Turn-out tends to be low.

But these two tightly fought contests may well assume greater political significance  than ever before in the UK’s electoral history. The outcomes on Friday morning may well tell us whether Labour can survive as a major political force in the land. And whether UKIP will become a key player in the British geo-political landscape.

There’s a long history of volatility in by-elections which goes back to the 1960s. The Liberals achieved a stunning victory in Orpington in 1962 by taking a solid Conservative seat. Some popular, newly elected MPs, who have won big in a by-election, fade from view by the time of the next general election. Their victory is often based on the apathy of government supporters who may have abstained from voting or flirted with one or more of the main opposition parties.

Between 2010 and 2015, the Conservative-dominated coalition government suffered some spectacular defeats, but went onto to win the 2015 election with a ten-seat majority. The Lib Dems paid a heavy price that year with a collapse in their share of the vote, ending up with eight MPs, down from 56!

For voters, there’s a big difference between a general election and a by-election. Contrary to popular belief, the electorate are highly sophisticated. They don’t treat these two plebiscites in the same way. In a by-election, the punters know that they’re not picking a government and feel free to give the ‘ruling elite’ a timely reminder of their dissatisfaction. Traditionally, voters use by-elections as a ‘protest vote’ against the sitting administration in Westminster. Until now, most by-election results  experience significant ‘swings’ from the party in government to the parties of opposition.

If a government lacks a clear majority, by-elections become more important. The loss of a seat could threaten the Government’s majority and its ability to rule. In 1992, John Major’s Conservative Party won with a 22 seat majority over Neil Kinnocks’s Labour. Five years on, Major’s slender majority had whittled down to one, due Labour winning a succession of seats in by-elections. By 1997, New Labour under Tony Blair won big with an eye-watering 179 majority over the Tories.

Local issues and the personality of the parliamentary candidate may on occasions be more important than usual in shaping the outcome in a by-election. The able and popular local council leader, Jim McMahn, increased the Labour majority in the Lancashire town of Oldham, a constituency which UKIP had hoped to take.

In the last two decades, there’s been a lot of ‘tactical voting’ going on. This occurs when an elector votes not for their favoured party or candidate, but for another party which has a better chance of winning. This happened in the prosperous seat of Richmond Park last winter, where Labour voter (and members) abandoned their own candidate to back the pro-Remain Lib-Dems to see off the Brexit supporting Zac Goldsmith the former Conservative MP for the area.

Yet some commentators have argued that electoral behaviour has become more fluid and unpredictable. Party loyalties – ‘partisan de-alignment’ and the close link between social class and party – ‘class de-alignment’ is crumbling. Voters have become consumerist, shopping around for the best product.

In an era of post-Brexit, post –truth politics, some voters may protest not just against the sitting government, but against the official opposition. For Labour to lose Copeland to the Conservatives and Stoke to UKIP would be unprecedented in British political history. Both seats have been strongholds since 1945.

Writing in 2010 the political scientist Peter Riddell cautioned about placing too much emphasis on by-election results. They are a poor guide to what happens at future general elections. Over half the 24 seats which changed hands at by-elections – 1983 to 2009 weren’t held by the winning party at the subsequent general election.

Their main impact, he maintains, is on party morale and the national mood. The unexpected Conservative win at the former railway town of Crewe in 2009 depressed Labour. The party failed to win the seat back in in 2010 and 2015. In 2015, the Conservative MP increased his majority!

Labour losing both by-elections (as predicted by some bookies) would put Jeremy Corbyn even more on the defensive and plunge scores of Northern Labour MPs into deeper despair and turmoil. The parliamentary by-election may assume a greater importance than ever before.