One of the best destinations for Scuba Diving in Europe are the Canary Islands. There are quite a number of dive centers on the island. This is a compiled list, which shows Name, Homepage, Diving Associations, whether or not they offer Technical Diving (+Rebreathers), how far you can get certified (Divemaster, Instructor etc) and what Specitalties they offer.
There are a couple more dive centers but I only listed those that the official list of the Gobierno de Canarias because those are definitely legal. There might be others who didn’t make it onto the list yet and operate with a temporary license (so they are legal) but it’s hard to tell.
Scuba Diving Centers Gran Canaria
Feel free to let me know if I made mistakes or you want to add a divecenter/course.
I can personally recommend diving with Leagues Ahead Diving in Maspalomas.