Grey tabby found near Borough Market, blue collar

I found a cat this afternoon around 3:45pm near Borough Market on Southwark Street. It's a medium-sized grey tabby with a white chest and paws, short glossy coat, and bright green eyes; it's wearing a blue collar with a tiny bell and a white heart-shaped tag. There’s a small notch on its left ear and a faint nose scratch that might help ID. The cat was friendly and purring a lot, and I’ve kept it nearby here while hoping to reunite it with its owner—if this sounds like your cat, tell me about the collar tag or the notch.