A Liberal Democrat Cabinet minister has hit out at Tory Eurosceptics, claiming their ambitions for a looser relationship with Brussels would leave the UK "semi-detached" from the European Union with no say in the rules governing the vitally important single market.
Energy Secretary Chris Huhne warned that "if you are not at the table, you are on the menu" as the political fallout over David Cameron's controversial decision to wield the UK's veto over a new European treaty continued.
But there was support for the Prime Minister's stance from a group of senior business leaders, who cautioned against the UK being "dragged deeper into a more centralised and over-regulated EU".
In an interview in the Independent, Mr Huhne said: "A lot of the Conservative right pine for some semi-detached status where we would be like Norway or Switzerland - enjoying the benefits of the single market without being a members of the EU."
This would give "no direct influence" over European rules and would mean losing the "massive advantage" of being at the EU table.
"It is not in the national interest to be in a purely passive relationship, where our interests are being determined by other people," he said.
Mr Huhne, a former MEP, said that "a significant part" of the parliamentary Conservative Party did not understand how important it was to be involved in negotiations in Brussels.
"We need to make the case more positively. The case for our membership of the EU is not a case for ending national sovereignty but for delivering an age-old, historic objective of our foreign policy."
While acknowledging the EU was "too bureaucratic" and needed to change, Mr Huhne said: "That reform is much better argued from a position where you passionately believe in the benefits that can arise from EU membership than if your counterparts believe you have a hidden agenda which is essentially to destroy the EU and all its works."
On the eve of the crucial summit, there was a meeting of the European People's Party, the mainstream centre-right bloc in the European Parliament which Mr Cameron pulled the Tories out of.
Mr Huhne said: "You can't help wondering what would have happened if David Cameron had been there. If you are not at the table when things are being decided, you can't defend your interests.
"The phrase in Brussels is clear: if you are not at the table, you are on the menu."
But in a letter to the Financial Times, business leaders including JCB chairman Sir Anthony Bamford, Next chief executive Lord Wolfson, JD Wetherspoon chairman Tim Martin and Roger Bootle of Capital Economics dismissed fears of "isolation" as a result of Mr Cameron's stance.
The letter, orchestrated by think tank Open Europe, congratulates Mr Cameron for standing up for "an outward-looking and competitive Britain" by resisting the new treaty.
The 20 signatories said Britain does not want to be "dragged deeper into a more centralised and over-regulated EU with ambitions to become a political union" and Mr Cameron "deserves the full support of the business community".
"Those who would portray Mr Cameron's use of the veto as bad for jobs and growth or as leaving the UK 'isolated' are mistaken," the senior business figures wrote.
"The real threat to employment is the euro crisis, which was unaffected by his veto and which the recent summit did little to address. Britain has great potential to compete across the globe, if freed from badly targeted and trade-hampering government intrusions, whether from London or Brussels."
In a sign of diplomatic efforts to reduce the heat of the debate following the Brussels summit veto, a senior French minister has stressed the importance of the UK's relationship with France.
Foreign minister Alain Juppe said that he had "not an ounce of doubt" that Anglo-French relations would soon be excellent again.
President Sarkozy was reported to have branded the Prime Minister an "obstinate kid" for using his veto when he was unable to secure safeguards for the City of London at the summit.
And the diplomatic spat was heightened when Mr Sarkozy's finance minister Francois Baroin said he would rather be French than British economically, and Banque de France governor Christian Noyer suggested that the UK, rather than France, should lose its cherished triple-A credit rating.
But speaking to reporters, Mr Juppe denied that there had been a concerted effort by Mr Sarkozy's government to stoke up tensions with London.
The comments "went further than their authors wished" but there was "no need for excuses on either side", he said.
"There is not an ounce of doubt that Franco-British relations, that will become excellent once again as we have too much in common to allow them to deteriorate," said Mr Juppe.
"I don't think the bridges are broken. I cannot imagine that we will push Britain out of the European Union."