In case you don't know what was illegal (actually unlawful) here, it was the fact that he had a hidden agenda (to stifle debate). Proroguing parliament is not

In case you don't know what was illegal (actually unlawful) here, it was the fact that he had a hidden agenda (to stifle debate). Proroguing parliament is not unlawful, but using it as a tool to stop parliament exerting it's right - and then pretending it is for a different reason, is unlawful (the Supreme Court has decided) EDITED- removed: "that his reasoning by which he asked the Queen to close parliament was not truthful or honest" as this is not correct. The only unlawful bit was that he wanted to stifle debate: https://www.bbc.co.uk/news/uk-politics-49810261 https://www.bbc.co.uk/news/uk-politics-49810261 - "The decision to advise Her Majesty to prorogue Parliament was unlawful because it had the effect of frustrating or preventing the ability of Parliament to carry out its constitutional functions without reasonable justification."