I couldn't find Tesco's specifically, but in the basic foods section rotisserie chicken is 4.5 syns per 100g. The supermarkets put a sugary glaze on them to make them brown nicely, I expect that's why.
They used to be pumped with oil to make them more succulent (seemingly) so weren't free. However I think that practice has changed and they are free now provides you don't eat the skin x