If they are a RAS tenant, I would imagine they will be completely unable to pay the "full rent amount"...which will be what? How much of an increase will you be looking for?
You can ask them to leave but if they don't, and they do not have to until the notice period expires, you will not win a case against them for the new rent amount.
They have the right to stay until the end of the notice period, and you cannot force them to pay a new increased rent for the remainder of the notice period, and there is no way at all you will win such a case. Why make life difficult for yourself and them? You should have given them notice earlier so it coincided with the end of the RAS contract, that you did not is your mistake, not theirs. Safe yourself the trouble and Keep it at the RAS amount until the end of the notice period.