British people love curries and other spicy things. For most people curries, biriyanis are going to be in the rotation. Even “traditional” British food will usually have things like black pepper, nutmeg, mace, ginger, cumin, cloves, mustard, bay leaves, juniper berries in it. More recently cumin, paprika, tumeric, coriander, curry powder might be thrown into dishes.
Stole it? I think adopted is more apt. And curry isn’t one thing and varies from region to region in India. But Britain loved it so much that there is an Indian (or Pakistani) restaurant practically everywhere. And while Indian / Pakistani chefs have invented new dishes (e.g. chicken chasni is the best goddamned curry ever), I wouldn’t call it cultural appropriation.