There are distinct rules that VAT registered businesses must follow regarding retention of VAT records.
Generally, a business must keep VAT business records for at least 6 years (or 10 years if they use the VAT MOSS service). By special permission, HMRC may allow you to keep some records for a shorter period. For example, if the 6-year rule causes you serious storage problems or undue expense.
The VAT records can be held on paper, electronically or as part of a software program. There are no specific VAT rules about using a computer. Records used for other tax purposes may need to be kept for longer periods.
There are financial penalties that can be levied for a failure to keep or produce the VAT records required by law.
Regarding the issue of a VAT sales invoice: