Liz Truss is set to win the Tory leadership contest by a decisive margin next month, according to an exclusive Sky News poll that gives the foreign secretary a 32-point lead over rival Rishi Sunak.

The poll also shows that the legacy and personality of Boris Johnson is likely to loom large over the next prime minister as there is huge regret among Tory members over the decision to oust him in July.

The YouGov survey suggests 66% of members are voting for Ms Truss and 34% are backing Mr Sunak, once those who do not know or will not vote are excluded.

The race has tightened very slightly since a YouGov poll of members poll just over two weeks ago, when Ms Truss had a 38 percentage point lead.

Since then, there has been a series of testing television encounters between the candidates, including the Sky News special programme The Battle for Number 10, which ended with most of the audience backing Mr Sunak.

Yet the incremental improvement in his fortunes evident in this poll would be nothing like enough to rescue the contest for him.

Some 13% say they have not yet decided how they will vote or will not be voting. In the poll, which closed on Wednesday morning, 57% of respondents say they had already voted and 38% say they have yet to cast their ballot but still intend to.

Among those who have already voted, 68% chose Ms Truss and 31% Mr Sunak. Among those who are yet to vote, 44% say they will opt for Ms Truss, 29% say they will choose Mr Sunak while 26% say they do not know.

The poll makes clear that the incumbent prime minister is still held in high affection among Tory members and any successor could be unfavourably compared to him by Tory members.

In all, 55% say that Tory MPs were wrong to effectively force Mr Johnson to resign, while 40% say they were right.

If Mr Johnson was still in the contest alongside Mr Sunak and Ms Truss, 46% would vote for Mr Johnson, 24% for Ms Truss and 23% for Mr Sunak.

Similarly, 44% say that Mr Johnson would make the best prime minister, 24% Ms Truss and 23% Mr Sunak, and twice as many Tory members think Mr Johnson would beat Sir Keir Starmer in an election.

There are doubts about the likely victor’s ability to win the country. The poll found that 40% of Tory members believe a Truss victory would result in a hung parliament or a Labour majority, with worse numbers for Mr Sunak.

Another challenging area for Ms Truss if she enters government is evident in the poll over the issue of economic support to help the cost of living crisis.

Ms Truss has prioritised delivering tax cuts over tackling inflation. However, 63% say that the priority should be getting inflation under control, while 33% say the number one goal should be reducing people’s taxes.

And 65% of Tory members support a windfall tax – something Ms Truss is not keen on – while 31% oppose it.

Meanwhile, there is evidence of deep-rooted personal tensions resulting from the campaign in the poll.

Some 35% of the party membership say Ms Truss should not include Mr Sunak in her future cabinet, while 52% say he should, suggesting a large minority hold a highly negative view of the former chancellor.

YouGov interviewed 1,089 Tory members from 12 to 17 August for Sky News.