Rishi Sunak has surged ahead in the race to be Conservative leader while Boris Johnson was mounting a last-ditch scramble to shore up support among MPs, amid warnings his return as prime minister would lead to a political crisis within a week.

As more senior party figures cautioned that a Johnson comeback would lead to chaos and an early election, Sunak won the support of 150 MPs – just shy of the number needed to keep all but one other rival candidate getting on the slate.

Sunak launched his official campaign with a declaration that “fixing the economy” was his priority but he gave no media interviews or formal manifesto showing his proposed programme for government.  Penny Mordaunt, the third candidate, has also launched with about 27 backers, and gave an interview to the BBC’s Laura Kuenssberg saying she wanted to be a “halfway house” between Johnson and Sunak.      Related: Johnson, Mordaunt or Sunak: who is backing whom as next Tory leader     In contrast, Johnson had still not even formally declared he was running by Sunday evening. He had just 60 publicly revealed supporters, despite the claims of his allies to have reached the threshold of 100 Tory MPs needed.  Asked if Johnson had made it, one of his closest political friends said: “Yes. Verified.”  A leaked WhatsApp message from his campaign manager, Chris Heaton-Harris, told supporters: “I can confirm we have completed all paperwork to be on the ballot tomorrow.”