LONDON (Reuters) - Britain's deal on new terms for its membership in the European Union could be undone by the European Court of Justice despite support from all member states, according to Justice Secretary Michael Gove, a senior figure among those who want Britain to leave the bloc.
Gove faced a barrage of contradictory opinion, with Prime Minister David Cameron's Downing Street office, Attorney General Jeremy Wright and European Council President Donald Tusk among those saying he was wrong.
Considered a policy heavyweight in the British cabinet, Gove is a close friend and political ally of Cameron, but the men are on opposite sides of the debate before a June 23 referendum on whether Britain should stay quit the EU.
Gove does not have the popular appeal of London Mayor Boris Johnson, the most prominent member of the ruling Conservative Party to come out in favour of a "Brexit", but as Justice Secretary Gove's views on the legal issues will carry weight.
"The facts are that the European Court of Justice is not bound by this agreement until treaties are changed, and we don't know when that will be," Gove said in a BBC interview on Wednesday. "It's important that people also realise that the European Court of Justice stands above every nation state."
Downing Street issued a statement to rebut Gove's argument.
"It is not true that this deal is not legally binding. Britain's new settlement in the EU has legal force and is an irreversible International Law Decision that requires the European Court of Justice to take it into account," it said.
Attorney General Jeremy Wright, the government's chief legal adviser, also weighed in.
"It has legal effect from the point the UK says it intends to remain in the EU, and the European Court must take it into account," he said in a statement. That was not just his opinion but that of the government's lawyers, he said.
According to a YouGov poll published on Wednesday in the Times newspaper, 29 percent of people would trust Cameron on EU issues, while 17 percent would trust Gove.
The YouGov poll, conducted online, found that the "Leave" and "Remain" camps were neck and neck. A ComRes telephone poll published on Wednesday in the Daily Mail found the "In" camp was ahead by 12 points.
Tusk, who negotiated the deal with Cameron, told the European Parliament it was "legally binding and irreversible", in line with EU treaties, and "cannot be annulled by the European Court of Justice" (ECJ).
During a sometimes emotional two-hour debate in Brussels that pitted pro-EU members against eurosceptics from across the EU, that view was challenged by UK Independence Party leader Nigel Farage. He noted that the EU's supreme court would not be bound by inter-government accords that breached basic treaties.
Jonathan Hill, a Cameron ally who holds Britain's seat on Jean-Claude Juncker's European Commission, said on Twitter: "The ECJ has never overturned a clearly expressed binding agreement of all 28 leaders and EU presidents."
EU officials told Reuters that, while there was no formal advance discussion of new legislation with the ECJ, constitutional lawyers working for the EU executive and the judiciary had regular informal contacts.
An ECJ spokesman declined comment on the British debate.
Additional reporting by Elizabeth Piper in London and Alastair Macdonald in Brussels, editing by Larry King