Yeah; but they can't just ban British tourists outright, however much they would like to (British tourists incur a slight net loss; if we're not scamming the resorts with bogus illness claims, we're pissing, puking, shitting and shagging in the streets, which costs money to clean up and drives away other tourists) because Britain is also a member of the EU, and they would be in breach of several international treaties.
And EU rules are the reason why you're allowed to bring more than 20 cigarettes into the UK from anywhere else in the EU; since 1992, the single market and customs union means that as long as the duty has been paid in full in the country where taxable goods were first purchased, you cannot be held liable to pay duty anywhere else unless the goods change ownership.