Is it legal for businesses to have a minimum spend limit on cash sales?

right i know that they can have minimum spend limit for debit card sales but this is all sales including cash sales!!! ive been left so angry about a particular local shop who refused my payment of �4.80 because they issued a �10.00 minimum spend limit 2 weeks earlier and its not including vat.so including vat i would have needed to spend �12.