It looks like Screwfix's 'Clipsal Converta Socket Double to Triple' (12362) might be just what I want to solve a problem, but I don't know how it converts the double socket into a triple. The website description says 'No new pattress, fittings or wall chiselling required' so how does the triple fit? Does it fit into the double's box and extend beyond it at one end (or both)? Does it stick out from the wall much more than a standard socket?
TIA