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.