Parliament holds the full sovereignty of the United Kingdom. So it could pass a law that bars people found responsible for misconduct from serving as an MP. It could also pass a law saying "~~Bobby Sands~~ Nigel Farage is a criminal and criminals must not be MPs." But like all acts, the question is whether it can do that without being seen as undemocratic. Parliament could pass a law tomorrow that abolishes democracy and turns Parliament into an appointed body. It's never a question of whether Parliament can do it, but whether Parliament should do it.

And in full respect, I do think that Farage is a criminal and a fascist and should not be an MP. But my opinion does not matter, and neither does yours.

Remember, this man is the leader of a political party which until recently, if the polls are to be believed, was slated to govern after the next election. Can you disqualify him, regardless of his scandals and crimes, without seeming undemocratic? If the public wants to support a criminal, is it undemocratic to ban them? If you do ban him, but do not abolish democracy, will that just cause him to become even more popular? If so, will his successor actually abolish democracy when they get into office?

Putting Adolf Hitler in prison did not kill his movement. It made him even more popular, and he killed democracy in the Weimar Republic. Prosecuting Donald Trump did not kill his movement. It made him even more popular, and he is killing democracy in America. What do you think banning Nigel Farage would do?