Thoburn v Sunderland City Council [2003] QB 151

The appellant in this case was convicted of selling fruit not in metric amounts that was illegal in that time. In this case, it was held that EC treaty was supreme above the legal systems of the member states. When UK accepted it in 1972, it also accepted EU law to be supreme to national law and that this 1972 act was a constitutional act which cannot be impliedly repealed.
“… being sovereign, [parliament] cannot abandon its sovereignty. … [As it would do through impliedly Repealing the ECA 1972]