If all they have in their cage is a bowl, then they are not adhering to the 2006 Animal Welfare act -
Duty of person responsible for animal to ensure welfare
(1)A person commits an offence if he does not take such steps as are reasonable in all the circumstances to ensure that the needs of an animal for which he is responsible are met to the extent required by good practice.
(2)For the purposes of this Act, an animal's needs shall be taken to include—
(a)its need for a suitable environment,
(b)its need for a suitable diet,
(c)its need to be able to exhibit normal behaviour patterns,
(d)any need it has to be housed with, or apart from, other animals, and
(e)its need to be protected from pain, suffering, injury and disease.
You would be well within your rights to go in there and tell them that the pig needs enrichment and suitable food to include hay
I did this on Tuesday at a local pet shop and they couldnt get the hay bags open quick enough!