One of Britain’s best-known companies last night warned staff its future could be placed under threat if we remain in the EU.

In a highly unusual move, Tate & Lyle Sugars wrote to its 800 UK staff warning that ‘EU restrictions and tariffs’ had added £30 million to its raw material costs last year.

This turned ‘what should have been a good profit, that we would all share, into a £19 million loss’, the firm said.

Gerald Mason (right, with Zac Goldsmith, centre, on a visit) told staff that EU tariffs on a single boatload of cane sugar could top £2.5 million. In a highly unusual move, sugar giant Tate & Lyle (pictured, north London) wrote to its 800 UK staff warning that ‘EU restrictions and tariffs’ had added £30 million to its raw material costs last year.

The company’s senior vice-president Gerald Mason told staff that EU tariffs on a single boatload of cane sugar could top £2.5 million.

He said the situation was made worse by the fact that Brussels officials ‘then send that money to subsidise our beet sugar-producing competitors in Europe’.

In a further damaging blow to David Cameron, Britain’s leading entrepreneur Sir James Dyson last night stepped up his call for Britain to leave the EU, warning that remaining in the Brussels club would be ‘an act of national self-harm’.

Sir James said the Prime Minister’s claim that Britain could go on to reform the EU was ‘pure fantasy’.

And he warned that the EU’s free movement rules had created an immigration system that made ‘no economic or moral sense’.

He went on: ‘There is a perception that having a seat at the EU table means Britain has influence. As David Cameron discovered in his recent attempt at renegotiation, we don’t.

‘There are 27 other countries at the same table with their own conflicting interests. It’s ungovernable and undemocratic. To think we can reform Brussels is arrogant and delusional - it is pure fantasy.’

The entrepreneur added: ‘I can confirm that we have no influence whatsoever in the shaping of Europe’s protectionist laws and regulations. Believe me, we’ve tried.

‘Consider immigration, which the United Kingdom should benefit from greatly. We need immigration, but we also need to be able to control it.

In a further damaging blow to David Cameron, Britain’s leading entrepreneur Sir James Dyson last night stepped up his call for Britain to leave the EU

‘It makes no economic or moral sense to ignore the world beyond Europe. Yet, we are forced to accept people from Europe without limit, while turning away economically vital engineers and scientists from the rest of the world.

‘This is the last opportunity to regain control of our futures. If we vote Remain, make no mistake, we lose control. This would be an act of national self-harm.’

The interventions threatened to overshadow a fresh effort by Downing Street to claim that business opinion is overwhelmingly in favour of staying in the EU.

Hundreds of businesses are expected to sign a No 10-inspired letter today warning that Brexit ‘would lead to uncertainty and put jobs at risk’.

But Boris Johnson yesterday accused the PM of using Government contracts and the promise of honours to persuade business leaders to back his campaign to keep Britain in the EU.

Mr Johnson said Eurosceptic business leaders were being ‘leaned on’ to keep their views quiet, while waverers were being tempted with the offer of rewards.

Speaking to LBC Radio, Mr Johnson said: ‘I can’t tell you the pressure that Project Fear and Remain put on senior business people not to articulate their views. Everyone has an interest in keeping friendly with government.’

Asked about the kind of pressure Downing Street was exerting, Mr Johnson replied: ‘I do not wish in anyway to be disparaging or critical of my friends in Government.

“But it is well-known that there is an operation in Downing Street and you will get a call from certain gentlemen, whose names you can discover.

‘And they will say, “look, you know, we want to continue to have contracts with you. It’s very important that we want to continue friendly relationships, there is an honours system as you know”, all this kind of thing. And that’s how it is. There is a bit of leaning on.’

Earlier this month, Mr Cameron was accused of ‘borderline corruption’ after using the Queen’s birthday honours to shower gongs on business leaders and luvvies who backed his campaign to keep Britain in the EU.

At least 20 prominent Remain supporters were rewarded with honours, including five company chiefs whose firms signed a previous pro-Brussels letter to the Times, six who signed a similar letter from entrepreneurs to the Financial Times and four members of the ‘creative industries’ who signed a No 10-inspired open letter backing the case for staying in the EU.

Recipients included Innocent drinks founder Richard Reed, who is deputy chairman of the official In campaign, Britain Stronger in Europe. Mr Reed, who describes the EU as ‘fantastic’, was rewarded with a CBE.

Downing Street denied handing out honours in return for support in the bitter referendum battle, saying a small number of Brexit supporters had also been honoured.

But No 10 does not deny orchestrating a series of letters designed to give the impression that business opinion is overwhelmingly in favour of remaining in the EU.

Tate and Lyle Sugars backed the Vote Leave campaign led by Boris Johnson, pictured, because of the impact of EU rules adding to the cost of the business

Downing Street aides have spent the last week twisting the arms of senior business figures to sign another open letter backing Britain’s EU membership.

An activist at the official Britain Stronger in Europe campaign has circulated business leaders with an email asking them to sign the letter which claims that leaving the EU ‘would mean uncertainty for our firms, less trade with Europe and fewer jobs’.

She identifies herself as ‘a special adviser to the Prime Minister (who is) now working for the campaign’.

Mr Cameron has also been piling pressure on wavering Tory MPs to speak out against Brexit.

In a series of one-to-one meetings, he has stressed the risk that Brexit could gridlock the Government for years.

One MP reported that the Prime Minister’s final plea had been: ‘You don’t really want three years of Euro-w**k, do you?’

Three more Conservative MPs fell in behind the PM yesterday - Jackie Doyle-Price (Thurrock), Caroline Nokes (Romsey and Southampton North) and David Tredinnick (Bosworth).

But Bristol North West MP Charlotte Leslie said she had decided to back Brexit.

Nick Herbert, chairman of Conservatives In, said a ‘clear majority’ of Tory MPs now back Remain, with 185 saying they want to stay in, compared with 143 backing Brexit.

Meanwhile, Michael Gove has compared economic experts warning about Brexit to Nazis who rubbished Albert Einstein’s scientific findings during the 1930s.

Mr Gove has faced criticism for saying voters have had enough of listening to economic experts issuing doom-laden warnings about Brexit.

Asked about the comments last night, he told LBC: ‘I think the key thing here is to interrogate the assumptions that are made and to ask if these arguments are good.

‘We have to be careful about historical comparisons, but Albert Einstein during the 1930s was denounced by the German authorities for being wrong and his theories were denounced and one of the reasons of course he was denounced was because he was Jewish.