They had already tried to make a claim, or at least informed you of that intention, so I would send them a form or ask them to complete one and then apply the normal HB rules to claim dates.
What you probably should have done at the time (I brought this up on another thread a while back) is refuse HB based on the UC regs that says HB is not payable and give them appeal rights, any appeal can't succeed. Now I/S has been awarded you would then have only needed to revise the previous decision.
This only works if he had not made a UC claim on 14, 15 or 16 of Feb though.
http://www.legislation.gov.uk/uksi/2014/1230/regulation/6
See regs 5 and 6.
