So the outcome,
The credit check was carried out on the 18th of April, 12 days after the policy was renewed and the broker notified on the 20th of decline. The broker, emailed, SMS and wrote to my Daughter that day addressing the urgency and giving 7 days to arrange alternative payment. On the 28th of April the Broker issued a letter of cancellation of insurance which takes effect from the 4th of May.
On the 1st of May my Daughter decides to ring broker "god only knows why she left it so long' -"Head - Sand - Buried" springs to mind and cancels the policy herself. Time on cover charge is £85 and broker fee is £257.00.
I have advised my Daughter to set up a payment plan with them to pay off the debt.
I still think 12 days to carry out checks and 2 to notify is fishy, but I can't prove anything.