British Prime Minister Theresa May arrives to meet with German Chancellor Angela Merkel at the chancellery in Berlin, Germany December 11, 2018. REUTERS/Annegret Hilse

LONDON (Reuters) - Some lawmakers in Prime Minister Theresa May’s Conservative Party are confident that enough letters of no-confidence have been submitted to trigger a leadership challenge, the deputy political editor of Sky News said on Tuesday.

“My ERG sources pretty confident now that 48 trigger been breached,” Beth Rigby said on Twitter.

A leadership challenge is triggered if 48 Conservatives write such letters to the chairman of the party’s so-called 1922 committee, Graham Brady. May could be toppled if 158 of her 315 lawmakers vote against her.

“Of course Sir Graham won’t announce while PM out of country - and we’ve been here before. But mood hardening,” Rigby said.

The European Research Group (ERG) is a group of Euroskeptic British lawmakers.