He announced Labour's two-pronged plan to reduce the number, saying legislation would be passed to punish "bad bosses" who hire foreign workers and to educate more British citizens.

Last year's net migration of 685,000 was the second-highest in the history of the country.

On Sunday, Sir Keir stated to The Sun, "Read my lips: I will reduce immigration."

"If you trust me with the keys to No10 I will make you this promise: I will control our borders and make sure British businesses are helped to hire Brits first.”

He added: “This is a changed Labour Party, back in the service of working people.

“That means not just talking about sky-high migration but acting on it.”

The Sun on Sunday can reveal that the Labour Party would bring in two big legal changes to cut migration.

Bad bosses who break employment law — for example by failing to pay their staff the minimum wage — will be banned from hiring workers from abroad.

Training will also be linked to immigration, so sectors applying for foreign worker visas must first train Brits to do the jobs.

This will also help bring down the bloated benefits bill, Sir Keir added.

It is the first time that the Labour leader has publicly committed to curbing immigration if he becomes PM.

His remarks - his hardest hitting ever on immigration - parks Labour tanks firmly on Tory lawns.

His remarks — his hardest-hitting ever on this massive election issue — park Labour tanks firmly on Tory lawns.

Sir Keir refused to say what he would cut migrant numbers to, or by when.

Instead he took aim at Tory PMs from David Cameron onwards for promising but failing to cut numbers.

Instead, he took aim at Tory PMs from David Cameron to Rishi Sunak for promising but failing to cut numbers.

Speaking on Friday as he visited the Port of Greenock, near Glasgow, Sir Keir insisted: “I’m not going to duck the challenge. It’s got to come down.”

He added: “The 685,000 migration ­number — it’s the second highest on record.

“We are near Glasgow and that’s more people than the entire city of Glasgow.

“The Conservatives repeatedly say they are going to cut these numbers. They have never done it. They have completely failed. They have never had a strategy to deal with it.”

He said bosses have become “too reliant” on foreign workers and must be weaned off immigration.

Sir Keir said: “You should always have a choice of recruiting a British worker first.

He said passing laws to curb sky-high immigration would be a top priority.

At the centre of his strategy would be legislating to link the immigration system to training.

When businesses ask for foreign work visas to be doled out, it would automatically trigger a plan to instead train Brits in those trades.

This would be done by bringing together the Migration Advisory Committee, the Industrial Strategy Council and Skills England.

Alongside this would be the tougher approach to bad bosses who flout employment law by under-paying British workers or by breaking health and safety regulations.

Guilty employers would be banned from hiring overseas workers.

In a direct warning to these dodgy bosses, Sir Keir said: “If you undercut, if you don’t do the right thing, we’re not going to slap you on the wrist. We are not going to fine you.

“We are going to ban you.”

Sir Keir’s remarks risk kicking off a war with the left-wing of his party.

His words show that despite being more than 20 points ahead in the opinion polls, Labour are worried their old reputation for being soft on borders could end up harming them at the ballot box.

It comes as the election campaign stepped up a gear with the launch of the Tory and Labour battle buses.

If the polls are correct, Sir Keir will be the first Labour leader since Tony Blair to win a General Election.

The 61-year-old has been accused by some of being a “copycat Blair” — hiring his old staff, wrapping himself in the flag like the Blairites did and even adopting the same look by rolling up his shirt sleeves.

But on immigration he is adopting a very different tone.

So does he think Mr Blair was wrong to not be tougher on borders?

Sir Keir said: “Circumstances have changed. That was a different era.
“I think, whether it is on immigration or more generally, security is a much greater concern for everyone.”

In a wide-ranging interview, the Labour leader repeated his pledge not to raise income tax, National Insurance or VAT.

But he refused to rule out introducing new green levies on bills.

He said: “What I can guarantee is this: we recognise this shouldn’t disproportionately impact people, particularly people who don’t have a lot of money.

“I’m not in an instant going to say there will be no such thing as a levy ever again.”

Sir Keir has another four and half weeks on the road before election day on July 4.

Labour are so worried about throwing away their poll lead that staffers have been banned from ­saying the word “win” in case it breeds complacency.

A few months ago, Sir Keir had dinner with his hero — former Arsenal manager Arsene Wenger.

Sir Keir said: “He is a great man who fundamentally changed football.”

Under Wenger, Arsenal famously went undefeated throughout the 2003-04 Premier League season — earning the nickname The Invincibles.