There was an English restaurant but it closed down.
Granada has some great food options and it would be a pity to not try Spanish food.
A lot of Spanish restaurants would make something something special for your father as long as it is simple.
If you explain to them that your father has a delicate stomach they could make something sufficiently bland.
Maybe boiled potatoes, some peas and a pork chop.
Most platos combinados restaurants have food that is very international.
Of course you could go to burger king or Macdonalds.
Page about British food
https://lingolex.com/cc/foods.htm Image of someone trying British Food.
Yorkshire pudding