Assessment of earned income for furloughed employees

Hi,

I have a client who will be most likely be furloughed in the next few weeks and be eligible to receive 80% of her wages under the job retention scheme. She already receives UC due to high childcare costs.
As the scheme is not likely to be ready for employers to access the grant until the end of April employers may not report any earnings until the grant is received which will lead to an increase on UC entitlement.
My questions is how will UC assess any earned income eventually reported via RTI,  especially the first earnings reported following the receipt of the grant which are likely to include backdate payments from whenever the employee was furloughed?
Many thanks