David Cameron has insisted he would take action to defend British national interests in Europe if a new fiscal deal between other member states threatens UK powers.

After an EU summit deal on a new treaty provision to tighten eurozone discipline, the Prime Minister moved to counter eurosceptic fears that his opposition is weakening.

At the last EU summit in December, Mr Cameron caused fury by vetoing a 27-nation treaty. He then warned that any changes the others made under their alternative fiscal pact - excluding Britain - could not use EU institutions such as the Commission and EU court because they could only carry out policies applying to all 27.