Weekly earnings paid on a monthly basis for HB/CTB purposes

My client works 40 hours a week without change or overtime. His earnings are paid the last Friday of every month. Therefore, some months he gets paid for five full weeks and other months he gets paid for four full weeks.

On his HB/CTB claim his earnings are being calculated as a monthly figure and he has a relevant change of circumstances every time he gets paid for a five week month, resulting in an overpayment.

I feel that his earnings should be input as a weekly figure not an average monthly figure, but the Housing Benefits Section disagrees.

If anyone else has come across this issue before or can offer any advice on how to resolve the issue, please comment.