Today I saw a big bus - with the diplomatic plate "251 D 141" from Britain. Very strage, I've never seen a 50-seater-bus with that. Unfortunately I couldn't see, from which country's embassy it was. When I passed it, there was a little sign behind the driver's door (it was LHD), but I only could identify "....Embassy" and as adress "Kensington Gardens"

Is it possible at British diplomatic plates, to identify, from which embassy the vehicle is?