DLA, JSA (IB) & the Disability Premium

My client has been in receipt of JSA (IB) for 2 years now and has only recently won his appeal for DLA - Lower Rate Care only - the DLA claim was made nearly a year ago. Consequently his JSA now includes the Disability premium but only from the DLA award date. Can anyone tell me if my client is entitled to have the DP backdated to the original DLA claim date or not and why?

Yes it should be backdated to the date that DLA started.  See Regs 6(2)(e) and 7(7)(a) Decisions and Appeals Regs 1999.  Appeal the current decision awarding the DP from the later date and ask the tribunal to make the decision which the DM should have made under the above regs.