JEREMY Hunt’s plan to cut corporation tax would give Scottish businesses a £1.3 billion annual boost with each company saving £1,300 a year, the Foreign Secretary insisted today.

Boris Johnson, meanwhile, made clear he planned to stop the rollout of so-called “sin taxes,” duties on cigarettes, alcohol and sugar, until it could be clearly demonstrated they made a real difference to people’s behaviour and did not unduly penalise the lowest paid.

With three days to go before postal votes drop in the letterboxes and in-boxes of the party’s 160,000 members, both candidates are continuing to push out policies in the hope of convincing the undecided to vote for them.

One of Mr Hunt’s key pledges is to slash the tax on company profits from 19 per cent to 12.5 per cent, costing £13bn a year.

He estimated that a Scottish firm making a profit of just £20,000 a year would pay £1,300 less if corporation tax were cut to 12.5 per cent.

“As the first entrepreneur to become Prime Minister, my government would back business like never before,” declared the Secretary of State.

He said for a “company struggling to get by in Nicola Sturgeon’s anti-business environment,” a £1,300 annual tax cut could be the “difference between success and failure”.

Mr Johnson, still maintaining his lead as the frontrunner, insisted it was time to “halt the explosion” of sin taxes and pledged not to increase them until a comprehensive review into their effectiveness had taken place.

He said: “The recent proposal for a tax on milkshakes seems to me to clobber those who can least afford it. If we want people to lose weight and live healthier lifestyles, we should encourage people to walk, cycle and generally do more exercise. Rather than just taxing people more, we should look at how effective the so-called ‘sin taxes’ really are, and if they actually change behaviour.”

The former London Mayor added: “Once we leave the EU on October 31, we will have an historic opportunity to change the way politics is done in this country. A good way to start would be basing tax policy on clear evidence.”

Earlier, both candidates addressed a hustings in Northern Ireland, where Mr Hunt insisted the Irish backstop proposal had to "change or go".

He said the problem with the backstop was that it would "trap" the UK into following EU customs tariffs until the EU gave its permission to leave. "For a Brexit vote that was about bringing back sovereignty that is not acceptable," insisted Mr Hunt, who believes the use of technology can maintain the open border.

Mr Johnson told Tory members in Belfast that it was “absolutely vital” to stress two things.

"Number one: that we will under no circumstances have a hard border. There will be no physical checks or infrastructure at the border in Northern Ireland.

"And number two: we will make sure we have an exit from the EU, a Brexit, that allows the whole UK to come out entire and undivided and we keep our union absolutely intact."

Later, Mr Hunt conceded a no-deal Brexit could be almost as bad as the 2008 financial crisis, telling ITV News: “The Bank of England's predictions are that it wouldn't be quite [as bad as the financial crisis] but it could be very serious if we get this wrong."

Meanwhile, the Foreign Secretary took the BBC to task for offering a head-to-head debate with Mr Johnson on July 16 ie after the ballots had been delivered to members.

He tweeted: “Absolute joke to give the appearance of a debate whilst knowing it can have ZERO influence on campaign."