LONDON (Reuters) - Britons are politically more divided by age than at any time over the past four decades, with a surge in support for the opposition Labour Party among younger voters the key factor in a shock election result, pollster Ipsos Mori said on Tuesday.

FILE PHOTO: Jeremy Corbyn, leader of Britain's opposition Labour Party, gives an election campaign speech in Basildon, June 1, 2017. REUTERS/Neil Hall/File Photo

Conservative Prime Minister Theresa May lost her parliamentary majority in the June 8 election after a lackluster campaign during which her poll lead of 20 points or more evaporated.

The Conservatives still won the largest number of House of Commons seats, but are now having to seek a deal with a small Northern Irish party to support their minority government.

Ipsos Mori said age was a bigger dividing factor than in any election since it began keeping detailed records in 1979.

It said Labour increased its share of the vote among people aged 18 to 34 by 20 percentage points, while the Conservatives lost support.

May’s party picked up vote share among older voters, achieving a 7-point gain in the 45-54 age group and a 14-point increase in voters aged over 55.

An increase in turnout among younger voters, compared with the previous election in 2015, was also crucial.

“Compared to 2015, turnout rose most among young people, to match their estimated turnout levels in the EU referendum, while it fell very slightly among older people – but older people were still much more likely to vote overall,” Ipsos Mori said.

As well as age, Ipsos Mori said class was a factor in the outcome, with more middle-class voters, who usually favor the Conservatives, choosing Labour, while the opposite trend was seen in lower-income groups.

The findings chime with much analysis that has appeared since the election, focusing on the generational divide.

Political analysts have said younger voters, who are facing challenges such as record-high university tuition fees and housing costs, were enthused by Labour leader Jeremy Corbyn’s youth-friendly policies such as abolishing tuition fees.

In contrast, older voters, who are more likely to own homes and to have benefited from decades of rising property prices, were far more receptive to the Conservatives’ message of low tax and fiscal discipline.

Both main parties increased their share of the national vote compared with 2015, at the expense of smaller parties. But Labour’s share increased by 9.5 points to 40 percent, while the Conservatives’ increased by 5.5 points to 42.4 percent.

Under Britain’s first-past-the-post voting system, the number of seats each party wins is determined by how they do in each of the 650 constituencies, or electoral districts. The stronger surge in support for Labour meant that some tightly contested seats went from the ruling to the opposition party.

Overall, the Conservatives lost 13 seats, while Labour gained 30.