The latest Opinium survey shows that Ms Truss has a healthy lead over Mr Sunak in the Tory leadership race, ahead 61 per cent to 39 per cent among Tory members.
But the poll shows signs of regret at the PM’s political demise over the Partygate scandal, and an apparent lack of enthusiasm for either of his would-be successors.
In a head-to-head contest between Mr Johnson and Ms Truss, 63 per cent of Tory members would opt for the caretaker PM, compared with 22 per cent support for the foreign secretary.
Results were even more stark in a Johnson versus Sunak contest. Some 68 per cent of Tory members prefer the PM over the ex-chancellor.
A separate Savanta ComRes poll for The Independent also found evidence of “Johnson nostaligia” among 2019 Tory voters.
If the caretaker PM were running as a candidate, 46 per cent of Tory voters would prefer he won, compared to only 24 per cent for Ms Truss and 16 per for Mr Sunak.
When it comes to the leadership race, Ms Truss is the favoured choice as the next PM among 49 per cent of Tory voters, compared to Mr Sunak on only 25 per cent in the Savanta poll.
Mr Sunak has vowed to keep fighting despite his underdog status, with his team claiming that he is “making progress” in winning over undecided voters.
A Sunak campaign source said: “This was always going to be a tight race and Rishi is working hard to earn every vote. Only a week or so ago a different poll had the gap wider and Rishi is clearly converting undecided voters.”
It comes as Mr Johnson reportedly plots a possible comeback as prime minister if his successor implodes.
The Sunday Mirror cites a “Westminster insider” claiming that the caretaker Tory leader is determined to stage a return to No 10 in future.
And a Tory party source said calls for a Johnson resurgence “could well intensify if things go badly for Liz – you get people thinking ‘Would he have been any worse?’”.
Dismissing the speculation, Jacob Rees-Mogg has played down the chances of Mr Johnson ever returning as prime minister as unrealistic.
“Nobody’s come back having lost the leadership of a party since Gladstone, and I just don’t think that, in modern politics, the chance of coming back is realistic,” he told GB News.
The Brexit opportunities minister added: “Lots of people think they’re going to be called back by a grateful nation, which is why Harold MacMillan waited 20 years before accepting his peerage. Life just isn’t like that.”