Boris Johnson took the decision to prorogue parliament for five weeks in the run-up to Britain's deadline for leaving the EU on October 31. His government argues that he was legally able to do so. The preceding parliamentary session was the longest on record and the prorogation was designed to bring it to a natural close. Opposition MPs believe Johnson's motives were to stymy debate and were, therefore, unconstitutional.
No, it was illegal
Johnson's decision was without legal precedent and in breach of the British constitution. It was illegal in the purest sense of the word.
Boris Johnson was in breach of the British constitution
The constitution does not allow a Prime Minister to prorogue parliament for the purpose of stymying debate and bypassing the democratic process.
Parliament is the master of its own fate and as the leader of the majority party in parliament, Boris Johnson was well within his rights to bring the longest parliamentary session in history to a close.
Parliament is the master of its own proceedings
Parliament alone decides when it will sit and when it should be prorogued. As leader of the majority party, Boris Johnson is allowed to prorogue parliament whenever he chooses.