If Britain pulls out of the European Union it would spell disaster for countries like Poland, the country's ambassador has warned.
Witold Sobkow, the country's representative to the United Kingdom, told a conference of businesspeople on Tuesday that "no arrangement other than full membership" of the European Union can offer similar benefits to fellow European nations".
Speaking at the British Chambers of Commerce conference in London, he went on: "We'd like to see the UK being an active member of the EU, shaping the policies of the EU. We agree eye-to-eye on most things when it comes to the single market."
He warned that a British exit could spark more uncertainty for businesses. "If Britain left the European Union, it would be a disaster for countries like Poland because we would lose the balance we had," he said.
The Prime Minister has pledged to renegotiate Britain's position in the European Union, with the aim of putting the new offer to voters in an In/Out referendum by 2017.
However, John Longworth, director general of the British Chambers of Commerce, is set to use his speech today to warn that the debate on Europe has been “hijacked by political ideology”.
“We need to bring the referendum date forward because two-and-a half-years of uncertainty isn't good for growth and investment,” he told the BBC ahead of his speech.
Meanwhile, Labour's shadow chancellor Ed Balls used his own speech to accuse the Tories of causing “uncertainty and risk for British business” with their referendum plan. “Britain walking out of the EU is the biggest risk to our economy in the next decade,” he said. “EU exit risks British jobs, trade and investment and the future prosperity of the UK"
"Britain must lead the debate for reform in the EU. Banging the table for change and for the EU to work better for Britain. But not flirting with exit and putting party interest above the national economic interest."
See more on General Election 2015
George Osborne has sought to downplay concerns about the coalition's renegotiation plans. He told Bloomberg Business TV: "We've made it clear that Britain wants to stay in a reformed European Union. The European Union needs to change so that it's a continent where jobs are created, prosperity is created. We also need to make sure that the relationship with members of the EU who aren't in the euro, like the United Kingdom, is a fair one.
"There has been a lot of talk, often in the media, that somehow our European policy might deter investment.
"The truth is, since we set out our policy we've continued to receive a huge amount of investment into the United Kingdom - more than much of the rest of Europe put together - and we are now a real go-to destination for international investors because we have a competitive tax system, we've got a skilled workforce, it's a great place for start-ups to grow a business."
This comes as Cameron ordered businesses to give their employees pay rises, but a union leader has condemned this as "pre-election mood music" and said the prime minister has presided over the worst fall in living standards since the Victorian era.
The Prime Minister will tell the British Chambers of Commerce annual conference that economic success should be demonstrated not just in the GDP figures but in the contents of workers' wallets.
Cameron, who hopes growing economic confidence will help him win the general election, will highlight the above-inflation rise in the minimum wage, as he tells bosses: "It's time Britain had a pay rise."
But TUC General Secretary Frances O'Grady dismissed Cameron's call, saying: "Since David Cameron became Prime Minister, the average wage is worth £2,500 less a year, the worst fall in living standards since Queen Victoria was on the throne.
"Saying it would be nice if wages went up is no more than pre-election mood music. If elected again his policies would do the opposite.
"Huge cuts would take spending back to the same share of the economy as in the 1930s. This would depress the economy and mean public sector wages would fall every year."