Liz Truss holds a commanding 22-point lead over Rishi Sunak in the race to become the next Tory leader and prime minister, according to an exclusive poll of party members for the Observer. With less than three weeks to go before the September 2 deadline for voting, the survey by Opinium of 570 Conservative members puts the foreign secretary on 61% and the former chancellor on 39%. Truss’s lead is, however, less than in some other recent polls of the Tory electorate, possibly suggesting that Sunak may have closed the gap in recent days. She has come under increasing pressure over her refusal to back what she describes as “handouts” to help people with their energy bills, and was heavily criticised for a U-turn over pay rises for public sector workers outside London and the south-east of England. Opinium’s detailed questioning also uncovers a striking lack of enthusiasm for either candidate when members are asked whether they would prefer one of them to Boris Johnson to run the party and country. When offered the choice of Johnson still being in No 10, or Truss taking over, some 63% of Tory members said they would prefer Johnson to be still in charge against 22% who wanted Truss. Even more starkly, 68% said they would prefer to still have Johnson than see him replaced by Sunak, who was preferred by just 19%. The poll found that almost three in ten of the Tory electorate (29%) had already voted. Some 47% said they would definitely be voting for the candidate they had opted for. Just 19% said they had yet to make up their mind. Opinium said that while these finding still meant it was possible for Sunak to pull off a stunning comeback and enter No 10, to do so he would have to win over almost all the undecideds and convert a sizeable chunk of Truss waverers. Truss’s support is particularly strong among older Conservative members, while Sunak’s is far higher among younger ones. Among over-65s Truss is 40 points ahead, whereas she is eight points behind Sunak among the under-50s. Advertisement Opinium asked members what the main single reason was that they backed one of the two candidates. For Sunak the most cited reason was that he would be better at managing the economy (22%), while 10% said they regarded him as the most competent or intelligent. A main reason mentioned by people who backed Truss was dislike of Sunak (14%). The same proportion (14%) said the foreign secretary was more honest and trustworthy, while 10% chose the fact that she had remained loyal to Johnson and not called on him to resign. Some 2% of Tory members cited race or ethnicity as a reason for supporting Truss and not Sunak. Chris Curtis of Opinium said that despite an apparent growing nostalgia among Tory members for Johnson – and a less than ecstatic response to either of the candidates bidding to replace him – it was now hard to see how Truss could fail to become the next prime minister. “From the moment we knew the final two candidates, it has been clear that Truss has had all the momentum, and our latest poll sets out just how large her lead among the party members has become,” he said. “With many members having already returned their ballot papers, it is now very unlikely Truss won’t become prime minister in September. “It’s clear that Sunak’s biggest problem is trust. While some members respect his economic arguments, this hasn’t been enough to overcome the view among members that he isn’t honest or trustworthy enough for the top job, particularly after he called for Johnson to go.” Today’s poll is the first by Opinium taken exclusively among the party members who will ultimately decide the next Prime Minister, since MPs whittled the number of candidates down to two. The final result will be announced on September 5.