Hi Marie
Welcome to the forum, you might want to have a look at the following FAQ which explains where everything is.
Welcome to Benefits and Work .
I believe DWP can offsetting a backdate payment against an overpayment:
www.gov.uk/government/publications/benef...yment-recovery-guide from reading comments on other forums a number people have stated that they were paid the full backdate in their bank account with no offsetting.
if you are relying on the backdate to pay for other things, you could ask DWP not to recover all of the overpayment.
PAOR Regs, reg 5 & 13; O&R Regs, regs 8 & 16
For more details about overpayments, read the notes to section 71 of the Social Security Administration Act 1992 in Social Security: Legislation 2019/20 Volume III
Gary