In my client’s case the UC claim was made on 13/09, and on 13/11 we requested backdating on the phone, and a letter from me setting out the grounds was uploaded to the journal.
On 04/12 the request was disallowed, reason given is that the backdate request was made too late.
The rules depend upon whether the claimant is of working age or pension credit age.
A claim for housing benefit for a claimant of working age can be backdated for a maximum of one month.A working age claimant must have a good cause (see below) for her/his late claim throughout the period for which backdating is requested.
It seems tough that for sick people you have to ‘reasonably been expected to make a claim earlier’ when they believed that advised them to make a new style ESA claim.
S/he only needs to qualify for housing benefit and be of pension credit age during the period in question.If a claimant of working age can show s/he has 'good cause' (a good reason) for not making a housing benefit claim for a period during which s/he was entitled to it, the local authority must backdate the claim.Examples of good cause might include if the claimant: If the housing benefit claim is for accommodation in a hostel where the rent is payable on a daily basis, the claimant does not need to show 'good cause'.
In all cases, housing benefit for a hostel is awarded back to the date that the claimant moved in.  reg 83(12A) Housing Benefit Regulations 2006 SI 2006/213 as amended by reg 3 Housing Benefit (Abolition of the Family Premium and date of claim) (Amendment) Regulations 2015 SI 2015/1857; HB Circular A3/2016. reg 64(1) Housing Benefit (Persons who have attained the qualifying age for pension credit) Regulations 2006 SI 2006/214 as amended by reg 5 Social Security (Miscellaneous Amendment) (No.4) Regulations 2008 SI 2008/2424. reg 64(1) Housing Benefit (Persons who have attained the qualifying age for pension credit) Regulations 2006 SI 2006/214. reg 83(12) Housing Benefit Regulations 2006 SI 2006/213. Part A2, para 2.510 DWP Housing Benefit Guidance Manual.
Useful tips and practical case studies are also included covering people who are employed and self-employed.
Further details, including allowable expenses, eligibility and claiming back tax for past years are also on the HMRC website.This backdate has been refused on the basis that they cant argue official error and that the illness didn’t prevent him making the claim as they had made a claim, albeit for the wrong benefit.