Labour and Lib Dem tactical voting plans will have big impact on Tory seats

According to MRP models, the Conservatives will win about 50 seats at next week’s election. Then again, some pollsters using the same method believe they are heading for closer to 200 seats. The same models show Labour heading for somewhere between 375 and more than 500 seats.

One reason for the huge variation in seat predictions is that people are preparing to vote tactically in historic numbers, encouraged by two opposition parties that have all but abandoned campaigning in each other’s target constituencies.

A poll by Ipsos on Wednesday showed that nearly one in five voters say they are planning to vote for a certain party not because they support it but because it is the one most likely to defeat the Conservatives where they are. That is more than any other general election campaign on record, when the numbers doing so tend to be between 10 and 12%.

Keiran Pedley, a pollster at Ipsos, said: “Tactical voting is set to be more widespread than normal, which is why the Conservatives are doing so badly in some seat projections. If you want to predict the scale of the Conservative defeat, you have to understand the impact of tactical voting.”

Labour and Liberal Democrat voters have often crossed sides to eject Conservative MPs at an election, but this time they are being aided in that choice by the decision by both parties to lead highly targeted campaigns focusing mainly on the Tories.

Both sides deny accusations they have done a secret deal not to challenge each other in seats where it might be close, but the impact of their campaign decisions has largely led to that outcome.

Ed Davey, the Lib Dem leader, has only campaigned in one seat where Labour has a chance of winning – Sheffield Hallam, which is a rare Labour-Lib Dem marginal. The central party has told local activists to make sure they are campaigning in one of about 80 Conservative seats, rather than any that Labour might pick up.

A Lib Dem source said: “Ed has been very clear that he sees it as his role to beat the Tories and get rid of this government. We have made clear to local activists that the campaign is based around being the challengers to the Tories in around 80 seats, and that is where they should be campaigning.”

Related: UK elections: what is tactical voting and how does it work?

Labour has a similarly disciplined approach to its campaign, forcing candidates and activists to move to seats they see as winnable even if they are far away. Some Labour members say they have even been locked out of their local voter databases in an effort to force them outside their own constituencies.

An analysis this week by the Financial Times showed that Labour campaigners had been diverted away from the 80 Lib Dem target seats. Activists in Somerset, for example, had been instructed to travel more than 80 miles to Plymouth, while London activists have been advised to ignore Lib Dem targets in the capital’s south-west.

One Labour frontbencher said: “This was all worked out right at the start. We weren’t ever allowed into Lib Dem-Tory fights. The strategy has been extremely targeted from the beginning.”

Labour sources say this is not a deliberate ploy to help their Lib Dem rivals, but instead reflects its determination to maximise votes in the seats likely to decide the election. It also reflects the fact that the Lib Dems are most likely to pick up seats from southern Conservatives, whereas the key to a majority for Labour lies farther north, in the “red wall”.

Related: Labour to bring in automatic voter registration under plans to boost franchise

There are signs, however, that Labour is pulling back its campaign even where doing so could help the Tories.

Labour has told Jovan Owusu-Nepaul, its candidate in Clacton, to move to the West Midlands to shore up support there, even though many activists are keen to campaign against Nigel Farage in the Essex seat.

Some believe that the tactical campaigning is further evidence of the deficiencies of the first past the post voting system, which leads to voters having to choose between parties they support and ones that have a chance of winning where they live.

Darren Hughes, the chief executive of the Electoral Reform Society, said: “Tactical voting is a morbid symptom of the distorting first past the post system used in Westminster elections that often forces people to vote for the least worst option, rather than for a vision of the country they want to live in.”