As far as I know, the actual socket is the same size as the one that has been fitted for years. However, it is deeper, but I suspect you are exaggerating 😉 If you had a really old socket, they are a bit smaller but its standard practise to update them to the newer larger type anyway.
You could pay for them to move it to a less prominent position, if its sticking out into the hallway you might try phoning them up and saying you are not happy with its position as its going to get knocked off the wall etc.
But otherwise, the only way to make it smaller would be to fit a rebated metal back box into the wall, although its probably not worth the effort as it only reduce the height by about 15mm.