The original JB you have quoted is in fact a Ceiling Rose, used as a JB, you are probably looking in the wrong section.I couldn't find one. That one pictured was from B and Q, and screwfix didn
Yeah, thanks. I'm going to consult a friend who is an electrician. Just to be on the safe side. No use causing a fire or giving people a shock by using it either.
The JB, if it is inaccessible needs to be maintenance free, so your best bet would be to employ an Electrician, messing with this could turn into a disaster.