Hello Martin, I am Keith, one of the experts on Just Answer, and pleased to be able to help you with your question.
Unfortunately this matter is one of the vagaries of VAT and insurance.
A possible solution here is to obtain a short term bank overdraft to cover the adverse cash flow position until the input tax can be reclaimed on the routine quarterly return, You can always ask HMRC for assistance, The Inland Revenue, who never dealt with VAT anyway, was absorbed into HM Customs and Excise who did to form HMRC some years ago. in this exceptional situation ask for such inputs to be accepted as a special case for reimbursement.
I am so sorry to have to rain on your parade.