Client is married and husband has been given permission to stay as long as he is not a drain on the public purse. Client and husband are living together and client claims IS and HB etc. Clients question is now that they are together does she have to claim as part of a couple or does the fact that he has not to be a 'drain' mean she should claim as a single person. Or is there some provision for such a case?

She needs to tell them about him but will not be given any extra (eg increased applicable amount, and premiums etc). Why is she getting IS? If as a lone parent then she now stops being one as he is living with her, so she'd need to claim JSA instead (might be ok if it's because of incapacity, I think). This is one of those where they get you both ways. If he works, which he is probably allowed to do as a spouse with 2 yr limited leave, then the income aggregation rules still apply, and if they have children she can claim CB, CTC and so on, but as this curious hybrid between having and not having a partner. See the summary on p1415 of the CPAG handbook.