Most ale enthusiasts (like myself) have preferences. Ales are like models - some are blonde, some are dark, some spicy, some subtle and drinkers, like photographers, prefer certain styles to others. Try and find out what your dad likes, otherwise you might buy some rare and expensive malty ale which ends up down the sink if he only likes hoppy, bitter ones - you want him to have a drink which ends up down the pan, not down the sink (unless your mum's in the bathroom all night ).
As his daughter, whatever you buy him will be special though.
First is to find an Ale your Dad likes I am 50 lol and it will be an ideal gift but don't worry to much, does he like light ale IPA India pale ale looks like lager or dark ale like Guinness ? Or bitter.
Morrison, Tesco and Sainsbury have a great selection of Ales all hand picked for their quality, however not sure how far from you but a company call barearts in Todmorden do a great selection of vintage ales Trever the owner has his own brewery almost next to the store wortha look. They also do online shopping and gift packs,