Stop and question powers in the UK would be tricky given that anyone subject to questioning, save for a few exceptions, is entitled to several legal protections.
Not everything needs a power or law behind it. There's no reason an officer can't engage anyone in conversation. That persons reaction may or may not lead the officer to determine they need to detain them for a search or even arrest them. Much of that comes down to experience and circumstance.
500N,
So which is it? Police are racist for searching too many people 'of colour' or Police are ineffectual for being scared to tackle gangs of abusers due to their race?