Open Plaques, enabling searches for the nearest “blue plaque” on a building. Only one for Stoke-on-Trent, so far, so I suspect coverage isn’t very complete…

There’s also Plaque Guide, which has (apparently) mapped most of London for plaques, and seems to have limited and possibly expanding(?) coverage elsewhere…

Or you could just search over 6,000 photos on Flickr tagged with “blue plaque”. There can’t be many that haven’t been photographed by the Flickr-ing public by now. And they’ll probably have given at least a basic indication of the location.