Just to preempt the “he should be in prison” comments, as this is a police inquiry he will not be required to resign unless he is found guilty and sentenced to more than a year in prison, and has run out of appeals.
Of course there is nothing stopping the Conservative Party from withdrawing the whip if they feel he is distracting from their work, but even then he can sit as an independent MP until he resigns, or the next election.
Innocent until proven guilty does apply even to politicians you don’t like.