British Prime Minister Theresa May’s Conservatives secured a landmark victory in a parliamentary by-election on Friday, boosting her hand ahead of upcoming Brexit negotiations as her rivals suffered damaging poll setbacks.

Copeland byelection

Conservative Party candidate Trudy Harrison makes a speech after winning the Copeland by-election in Whitehaven,Britain (Reuters)

The Conservatives captured the north western region of Copeland that Labour have held since 1935, the first by-election gain for a governing party for 35 years and a result which piles pressure on the opposition’s under-fire socialist leader, Jeremy Corbyn.

Although Labour avoided the worst-case scenario of two defeats, Corbyn is likely to face renewed criticism.

Despite long-running unrest within the upper ranks of his party, Corbyn is unlikely to face a fresh leadership challenge because he retains strong support among the grassroots Labour members who re-elected him last year after a botched coup.

“To win power to rebuild and transform Britain, Labour will go further to reconnect with voters, and break with the failed political consensus,” Corbyn said in a statement after the result.

In the central English seat of Stoke-on-Trent, Paul Nuttall, leader of the populist anti-EU UK Independence Party, failed to overturn a Labour majority despite almost 70 percent of the city’s voters backing leaving the bloc at last year’s referendum, casting doubt on his future too.

The Conservatives also increased their share of the vote in Stoke from the 2015 election.

The two results point to May’s tightening grip on political power following the Brexit vote, and will be used as evidence that her strategy of pursuing a clean break with the EU has stemmed rising right-wing populism without denting her ability to take votes from an increasingly left-wing Labour Party.