British business leaders have reacted angrily to David Cameron's decision to use his veto against an EU treaty.
Although the prime minister said he took the action to protect the City's interests, WPP chief executive and supporter of the coalition Sir Martin Sorrell said on Monday the UK's interests would be better served "inside the EU tent".
He told the London Evening Standard that the decision "seems to be more about politics than economics".
In his blog, Robert Peston quotes an anonymous business leader who says he is "anxious" about the move: "Margaret Thatcher was a constant thorn in the side of European leaders, but she never vacated the negotiating table; I am anxious by the implications of what the prime minister has done."
It came as the EU Economics Commissioner Olli Rehn warned the City would not be protected by Cameron's intervention.
"If this move was intended to prevent bankers and financial corporations in the City (of London) from being regulated, that is not going to happen. We must all draw lessons from the financial crisis, and that goes for the financial sector as well," he said in a press conference on Monday.
"I would also like to remind you that the UK government has also supported and approved the six-pack of new rules tightening fiscal and economic surveillance which enters into force on Tuesday. The UK's excessive deficit and debt will be the subject of surveillance like other member states, even if the enforcement mechanism mostly applies to the euro area member states."
Labour have argued the deal does not help the city - and that Cameron accepting the treaty would not have forced Britain to adopt an EU-wide Financial Transaction Tax (FTT), which it could have vetoed regardless.
Senior credit executive at Norddeutsche Landesbank Tom Brown said the model for the City of London "only works if it works for the European Union as a whole", in a letter to the Financial Times.
David Wootton, Lord Mayor of the City of London said there was a "risk" of the City being isolated following the government's actions: "There is a risk and we need to combat that by engaging in the discussions.
"The City is much more of an international centre than Frankfurt and Paris at the moment. There were reservations of exactly that nature when we didn't join the euro… It is a possible risk, it is a risk if we get it wrong but I don't think anyone, from the City of London to the prime minister's office want to get it wrong", he told BBC Radio 4's The World At One.