London (CNN) UK Prime Minister Boris Johnson may be gunning for a stronger mandate in Thursday's general election , but a seat projection has not ruled out his Conservative party failing to regain its parliamentary majority.

The latest estimate from British pollster YouGov has the Conservatives on track for a 28-seat majority, but the polling range stretches from 367 seats in Parliament to 311 -- below the magic number needed for a governing majority. This particular model for predicting the outcome of an election was correct in 2017 while other traditional polls were wrong.

Britain could wake up on Friday then, with what is known as a hung parliament -- its third in a decade.

What is a hung parliament?

A hung parliament occurs when no single party gains the 326 of 650 seats needed in the UK's parliament for a full governing share.

Instead of immediately triggering a fresh election, the party with the largest number of seats will usually first attempt to strike a coalition agreement or some other kind of deal with one of the smaller parties.

This could be undertaken as a formal coalition or through an arrangement known as confidence and supply. In this arrangement, a smaller party agrees to back its larger partner with crucial votes in return for policy influence but does not take ministerial seats.

It will be a struggle for Johnson to form a minority government or coalition. He burned bridges with Northern Ireland's Democratic Unionist Party (DUP), which previously propped up a Conservative government, by breaching one of its red lines: allowing the province to be treated differently from the rest of the UK.

Labour might find it easier to form a coalition, but at this stage is ruling out a formal agreement.

Any potential deal that Labour were to strike with the Scottish National Party (SNP) or the Liberal Democrats would require major concessions: be it another Scottish independence poll, a second EU referendum, or for Corbyn to drop the prospect of negotiating a new Brexit deal with Brussels.

Has this happened before?

Yes, there has been a hung parliament twice in the past decade.

The UK saw its first coalition government since World War II in 2010, when Conservative leader David Cameron teamed up with the Liberal Democrats -- helmed by Nick Clegg.