In a decision that badly undermines Boris Johnson’s authority, Britain’s highest court ruled unanimously Tuesday that the prime minister broke the law by suspending Parliament in a way that squelched legitimate scrutiny of his Brexit plan.

The historic move by the U.K. Supreme Court offered a ringing endorsement of Parliament’s sovereignty and slapped down what justices viewed as the legislature’s silencing by the executive.

The ruling upended the prime minister’s plan to keep lawmakers away until two weeks before Britain is due to leave the European Union. The Supreme Court said Johnson’s suspension was “void” and never legally took effect, opening the door for Parliament to resume its duties Wednesday morning as if nothing had happened.

House of Commons Speaker John Bercow welcomed the decision, saying citizens were “entitled” to have Parliament in session to review the government and enact laws.

The ruling also established that Johnson had involved Queen Elizabeth II — one of the most revered and respected figures in British life — by giving her improper advice when he sought her permission to shutter Parliament for five weeks.

The justices made clear they were not criticizing Elizabeth, who as a constitutional monarch was required to approve the prime minister’s request.

The British government said Johnson spoke to the queen after the ruling, but did not disclose details of the conversation.