I've got several Fray Bentos pies in my kitchen cupboard, as 'emergency standby' meals. All of the major supermarkets stock them but the best place to look for them is often discount stores, pound shops, etc where (when they can be over £2 elsewhere) they're often sold for just a quid. The current range is here:
http://www.baxters.com/product-range/fraybentos
See also Poundland's listings:
http://www.poundland.co.uk/food-and-drink/canned-food/canned-meat-fish-and-veg
I also have a few Vesta meals in my cupboard, as an occasional treat. (Yes, I know that they're rubbish really but I quite like some of them, although Premier Foods seem to have discontinued most of them now). Again, the best place to look for them can be discount stores, e.g.
http://www.poundstretcher.co.uk/vesta-chow-mein-152g?
but Asda, Tesco and Morrisons also stock the Chow Mein. (It looks like that might be the only type of Vesta meal still widely available).