Britain's decision to drop opposition over use of EU institutions for fiscal pact sets 'worrying precedent' But senior British officials reassured other EU countries on Friday night that David Cameron would not pick a fight over the issue during the summit, which starts today. Mr Hague said: "This group cannot cut across the EU treaties. If the use of the EU treaties at any point threatens Britain's fundamental rights under the EU treaties, or damages our vital interests such as the single market, then we would have to take action about that, including legal action. So we will reserve our position on the specific question about the use of the court. Downing Street denied that the Government had abandoned opposition to the 26 countries using the EU institutions. The countries signing up to the new treaty would be welcome to use the institutions so long as they did not "undermine" the European single market,she said. A Number 10 spokesman said: "The Prime Minister has always been clear that we would approach the issue constructively. The position hasn't changed. The fundamental principle here is Britain's national interest. Our national interest is to ensure that the single market is not undermined. The institutions are there to operate in the interests of the 27. If the single market, and therefore our national interest, is undermined, then we would want to take further action.