The QC representing Government-challenger Gina Miller at the Supreme Court's Brexit hearing has said the 1972 Act, which took the UK into Europe, does not allow for it to be overridden by prerogative power.
Lord Pannick QC told the court that ministers had no power to "nullify" the 1972 Act after it was enacted and take away statutory rights and obligations created under it "without parliamentary approval".
He said: "There is no relevant prerogative power in this context."
Lord Pannick said the question was whether Parliament had intended by later legislation to confer a new power to that effect.
"I say only the clearest of statements by Parliament to that effect could create a new prerogative power.
"I say post-1972 legislation is very far from containing any such clear statement."
ITV News reporter Olivia Kinsley is watching the court proceedings.