PM 'not backing down' over EU institutions
A cabinet minister has said he trusts the PM to stop eurozone countries using EU-wide institutions without the UK.
There have been reports that David Cameron is ready to allow members of a new fiscal pact to use the European Commission and Court of Justice.
But Iain Duncan Smith said the PM had "vetoed" that possibility when he kept the UK out of the deal in December.
Twenty six other EU states are expected to join the fiscal agreement which will be discussed at next week's EU summit .
Mr Cameron vetoed treaty changes involving all EU states in December, which were aimed at bringing about closer fiscal union within the eurozone to help tackle its debt crisis.
He argued that there were not sufficient safeguards for the UK.
At the time Conservative MPs urged him to ensure that institutions built for all 27 member states were not used by the new grouping of other EU states.
Mr Cameron told MPs at the time: "In the months to come we will be vigorously engaged in the debate about how institutions built for 27 should continue to operate fairly for all member states, Britain included."
He later told BBC Radio 4's Today programme he would do "everything possible" to stop other EU states from discussing the single market without the UK.
But he admitted there were "legal difficulties" surrounding the use of institutions like the European Commission and European Court of Justice.
On Friday the Guardian reported that senior diplomatic sources had said that while the government still had its reservations, there would be no attempt to block them and no quick legal challenge.
But Mr Duncan Smith told BBC One's Andrew Marr Show: "I wouldn't let speculation go too far.
"The fact is the prime minister vetoed them using the institutions and he has always said that veto was because we had no guarantees that what they are proposing would not damage the single market, or for that matter, would actually cause problems for the financial sector.
"We don't know what they are coming forward with yet. They still haven't completed their treaty and they aren't anywhere near signing and we don't know that everybody will go down that road with them."
He added: "I absolutely trust the prime minister on this, I know where he stands.
"He stands on the basis that we must protect the single market, we want them to get their economies sorted out because that's causing us problems over here, but we do not want them thrashing around to damage the very thing that we set up, which was the access to the market place and the free flow of capital in the financial sector."
Separately Lib Dem Deputy Prime Minister Nick Clegg has told Parliament's House magazine one of his staff would be joining the No 10 team at the summit.
Mr Clegg was critical of the veto in December, saying it was "bad for Britain".