This would be easy to do using an autohotkey script to copy the area under the cursor to clipboard and then open a web page related to it.
I wrote a little AHK script a while ago called SelectoSurf
which I use for similar purposes, you'd just have to modify it to open a web page that does a map search instead of a web search.
Or you could use Find and Run Robot
to do the same thing -- trigger on a hotkey, copy highlighted text under cursor to clipboard, and then open a web page searching for that text.
The first step however is to find yourself a mapping website where you can search for locations on a uk map, and which returns the results you want. Then post on this thread that url with the search part.
For example. you might say that the web page you want opened is: