i work with in a food company and actually sell into tesco as one of our big accounts, they will have a field day with this. Firstly you are well within your rights! you need to right a letter to the address on the back of the bag, should be tesco HQ in Cheshunt (if you cant find it let me now i have it as i send stuff there all the time) mention you have kept the snail and will post it once it is required, but hang on to it till then, and the bag you got it out of as it will have a 'lot' number which relates to which batch it was produced in and will speed up your claim and tracking process. If they have to recall the batch this will cost the producers a shed load..at least 40k Also play up how distrested you were upon finding it and that it put you of your meal completely. that you dont normally complain however this has really shocked you etc etc Hope that helps and if you find anything is fish ready meals please dont complain it give me such a headache lol