Which benefit has been overpaid.

Hi

Grateful for any thoughts.
Cl had to claim UC when moved property. Had been in receipt of CBESA and IRESA.
Both CB and IR ESA continued to be paid. UC took into account the CBESA but not the IRESA, so now client has overpayment of UC.
Why is it an overpayment of UC rather than an overpayment of ESA?

That will be one of your overlapping payments, at least to some extent.

When UC was claimed, ESA(ir) was abolished and should not have been paid any more.  According to Reg 10 of the UC(TP) Regs 2014, the wrongly paid ESA is taken into account as income in the UC calculation.  If this is done retrospectively rather than in real time, there will be a UC overpayment.

It only reverts to its legacy overpayment status to the extent that there is no UC against which to offset it.

Thanks, that was my fear. No official error argument!