LIZ Truss was given a massive boost in the race to be next PM when it emerged that up to eight in ten grassroots Tories have already cast their vote.
Senior party sources say the majority made up their minds before seeing either of the two candidates at the hustings.
They believe it will work in the Foreign Secretary’s favour as she was hot favourite to win when the ballot papers started landing on doormats.
Ex-Chancellor Mr Sunak insists he has been winning over thousands of members from his personal appearances at local party gatherings.
But with 80 per cent of votes in, he would effectively need every one remaining.
A Tory insider said: “Almost a third of people returned their ballot papers within a few days of them arriving.
“Now it’s nearer 80 per cent, so Rishi has his work cut out to win.”
A Cabinet source said: “I’ve heard the returned votes are in that ballpark. There’s one thing Tory members do well — which is to vote and to vote early.”
Ms Truss has been trying to woo MPs who backed Mr Sunak into her camp — so she can boast she has the backing of the Parliamentary party if she wins.
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With 20 days until the ballot closes, Mr Sunak is focusing on hoovering up all the grassroots votes.
He said: “We did six events yesterday and the same again today.
“We spoke to around 2,000 people last weekend and I’m giving it everything.”
He added that he had support from a “broad swathe of people”.
However, a survey by ex-Tory deputy chairman Lord Ashcroft found that voters are marginally more likely to back Ms Truss in an election.
But his research showed Labour would beat both by a significant margin.
In a blow to the SNP last night, Ms Truss vowed that if she wins she will take on the Minister for the Union role and put all four nations equally at the heart of her government.
She vowed to open new export markets for iconic UK products such as Welsh lamb, Scottish salmon and ships built in Northern Ireland.