How much could the polls change in the final weeks to election day?

In under three weeks, millions of people across the UK will be voting in the General Election.

Opinion polls continue to suggest the Conservative Party enjoys a strong lead over Labour.

The poll averages issued on Thursday put the Tories on 43%, with Labour on 29%, the Lib Dems 14%, the Brexit Party 5% and the Greens 3%.

What is the likelihood of the polls shifting decisively between now and election day?

The most recent two elections show things at this stage can quickly change.

May's strong and stable lead crumbles in 2017

Theresa May's Tory lead dropped in the final weeks in 2017 while support for Jeremy Corbyn's Labour rocketed by 10%. Credit: PA Graphics

At the same point in the 2017 election campaign, the polls showed the Tories on 47%, with Labour on 31%, the Lib Dems on 8%, Ukip on 5% and the Greens on 3%.

But on election day, the Tories finished on 43% – four points below where they had been three weeks earlier – while Labour had risen 10 points to 41%.

While the Lib Dems remained on 8%, both Ukip and the Greens dropped to 2%.

The change was enough to deny the Tories a majority and produce a hung parliament.

Cameron gets an unexpected late lift in 2015

David Cameron's Conservatives saw a late boost as Ed Miliband's Labour challenge fell away. Credit: PA graphic

There was movement in 2015 as well, albeit on a smaller scale and with different consequences.

Three weeks before polling day in 2015, both the Tories and Labour were averaging 34% with Ukip on 13%, the Lib Dems 8% and the Greens 5%.

These figures pointed to a hung parliament – but come election day, the Tories opened up a seven-point lead over Labour to finish on 38% while Labour ended on 31%.

Ukip, the Lib Dems and Green finished on 13%, 8% and 4% respectively.

This was enough to give the Conservatives a small overall majority in parliament.

What does it show us?

The pattern in 2015 and 2017 suggests a lot can change in the three weeks before polling day.

It also serves as a reminder that polls are not predictions, merely snapshots of opinion at a certain point in time.

(Note: all figures quoted above are for vote shares in Great Britain)