Sir Keir Starmer has told supporters this weekend he will stand in any Labour leadership contest that is triggered.
Until now, the prime minster and his allies insisted he would not walk away if one was held but there has been a big question mark over what he would actually do.
However, after Greater Manchester Mayor Andy Burnham said he would seek to enter any potential leadership contest, Sir Keir’s position hardened, the BBC understands – telling his supporters he would fight any challenge.
The prime minister, who still believes a leadership contest could plunge the country into chaos, said he had won a massive majority two years ago and a mandate that he was determined to deliver.