About eighteen months ago I reported on Tesco's capricious misuse of the word "Vegetarian".
Today, that entry has been linked from a forum which is discussing the same issue
A poster there writes about the moronic and dishonest response she got from Tesco, who said
I do apologise that you where shocked to find fish in a vegetarian product and I apologise for the upset caused.There is a vegetarian called a Pesco-vegetarians which means they eat fish, dairy and eggs..."Therefore, as the content of fish is suitable for some forms of vegetarianism, for example Pesco Vegetarianism, Semi-Vegetarianism and Macrobiotic Vegetarianism, we will continue to show our Vegetarian symbol on products which contain fish, so long as there are no animal by-products."
Based on this I would warn you to exercise extreme caution in regard to anything that the lying bunch of tosspots at Tesco say regarding what is in their food.