Err no jlcm. Legislation concerning meat products like the pork pie discussed does not allow the thawing of frozen products to allow them to be sold chilled. Food regulations do not allow it because it's potentially dangerous for the consumer to eat the product after thawing. M&S would be taken to the cleaners if it was discovered.
Nevertheless, leaving the legislation to one side for a moment, the pies could not be thawed without causing a water film on the inside of the cellophane or paper packaging and on the surface of the pie itself - the ice would thaw and the resulting water has nowhere to go as the packaging is sealed. A wet pie would look pretty unsavoury and if I bought one, I'd shop elsewhere next time.