Backdating a claim to ESA

We have a client who is not in receipt of any benefits, but has significant health issues - his GP has issued a backdated MED3, which pre dates our area becoming full service - so can he make a claim to ESA, backdated to before UC came in?

Also this client does not have any housing costs - lives with parents. However if he did I assume that, unless he can also backdate the HB claim that as he would need to claim the housing cost element of UC, and so the ESA issue would be irrelevant?

Thanks in advance.

See this thread which I think covers the scenario.

Backdating IR-ESA claim in full-service area