LONDON - 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 Eurosceptic British lawmakers.