Only works for countries that don't have a large "black" economy and HMRC spends a lot of effort tracking down smuggled tobacco - normally sold in the back bar of the less salubrious pubs.
There used to be separate departments for each, but they were merged years ago. This was a slightly odd move, as the revenue were people who were good at doing very detailed analysis of paper trails, whereas customs were people who were good at kicking down smugglers' doors.