Maternity pay from Poland and treatment as income for UC

My client is due to receive maternity pay from her Polish employer who is reimbursed through the tax system.
She and her husband are living in the UK and he is working here.

I need to know how the maternity pay is treated for UC.

Reg 55 of the UC Regs would suggest that it will be employed earnings.
I am hoping not to have to wade through the tax law referred to in the regulation.

If there is any doubt that it constitutes employed earnings, any thoughts on the Withdrawal Agreement assisting would be welcome.

Thanks