VAT is 6
and one govt site advises
"Generally, you must keep all your business records for VAT purposes for at least 6 years. Records that you use for other tax purposes may need to be kept for longer periods."
altho I cant off hand think of any ( IHT and seven ?)
but needless to say they dont have to keep every scrap of record relating to each transacton.
also what is needed for the tax man may not be needed for you - and unless you are in a court action they are not bound to disclose it