Prime Minister Theresa May was fighting to hold on to her job on Friday as British voters dealt her a punishing blow, denying her the stronger mandate she had sought to conduct Brexit talks and instead weakening her party’s grip on power. With no clear winner emerging from Thursday’s parliamentary election, a wounded May signalled she would fight on, despite being on course to lose her majority in the House of Commons. Her Labour rival Jeremy Corbyn said she should step down.

With 633 out of 650 seats declared, the Conservatives had won 308 seats and were therefore no longer able to reach the 326-mark they would need to command a parliamentary majority. Labour had won 258 seats. With talks of unprecedented complexity on Britain’s departure from the European Union due to start in just 10 days’ time, the pound sterling was hit by uncertainty over who would form the next government and over the fundamental direction Brexit would take.

“At this time, more than anything else this country needs a period of stability,” a grim-faced May said after winning her own parliamentary seat of Maidenhead, near London. “If … the Conservative Party has won the most seats and probably the most votes then it will be incumbent on us to ensure that we have that period of stability and that is exactly what we will do.”

After winning his own seat in north London, Corbyn said May’s attempt to win a bigger mandate had backfired. “The mandate she’s got is lost Conservative seats, lost votes, lost support and lost confidence,” he said. “I would have thought that’s enough to go, actually, and make way for a government that will be truly representative of all of the people of this country.”

Conservative member of parliament Anna Soubry was the first in the party to break cover, calling on May to “consider her position”. “I’m afraid we ran a pretty dreadful campaign,” Soubry said.

May had unexpectedly called the snap election seven weeks ago, even though no vote was due until 2020. At that point, polls predicted she would massively increase the slim majority she had inherited from predecessor David Cameron.

Instead, she risks an ignominious exit after just 11 months at Number 10 Downing Street, which would be the shortest tenure of any prime minister for almost a century. “Perhaps the most obvious conclusion is that the likelihood of the UK needing to request a delay in the Brexit process has risen substantially,” JPMorgan said in a note.