Connecting to test socket

[#1]

@ Chris,
OK, thanks.
@Anotherone,
think you're right.  I'll just have to saw the window frame unfortunately

[#2]

Can you post a pic of your master socket?

[#3]

Quote from: AndyH

Can you post a pic of your master socket?

Sorry Andy = don't quite know how I missed this.  I'll see if I can do a picture but in the meantime I'll attempt an explanation: the socket is on a window ledge next to a hall window, with the base of the socket resting on the ledge.  When double glazing was fitted the fitters put a new window sill in which went past the socket to a depth of just under half the socket, so they cut the sill around it and "joined" it with sealant on the front and side which meets the sill (an "L" shape).  As a result when I unscrew the socket I can't slide the cover off as it's wedged into place by the sill.  The only option I can see is to remove the offending section of sill, which will involve cutting it by around a centimeter or so.  Since I failed carpentry 101 I'm afraid the result is going to look less than completely professional

[#4]

Can you not get a blade/Stanley knife to cut the seal between the NT5e and sill, then force the front plate off?

[#5]

already tried that.  The sill's fairly tight against the box.  I'm reluctant to apply too much pressure in case I break the box.

[#6]

I know what I'd do.  
Buy another box online (in case I broke the original) and "relocate" it.