We don't send out separate receipts or invoices as these are a part of the certificate of insurance.
Quite often we get asked for 'VAT Invoices', which is amusing because there is no VAT on insurance. Instead you pay Insurance Premium Tax which unfortunately is not reclaimable from HMRC.
You'll find the amount you've paid, and the IPT (Insurance Premium Tax) paid noted on the Certificate of Insurance. Your accountant should accept this as a valid receipt.