only if you are not being charged vat,
push for a 'receipt' with their name and address on it.
if the receipt details vat, then the receipt must also show their vat reg number,
some traders who arent vat registered (legally below the compulsory threshold) still make out a receipt along the lines of
amount �100.00
17.5% � 17.50
Total �117.50
the '17.5%' does not state it is vat and may be a 'service charge' so a nice bit iof extra profit!!!!
if vat is mentioned the receipt must comply! otherwise contact hmrc with the details because technically you cant claim vat back if you want to without a proper vat receipt