I need to move a double electric socket about 2 ft. The only problem I
foresee is that the area where I want to move the back box too is
thermolite bricks which have been laid to block up a door way.

Thermalite is so light and soft, you could dig it the chase with a teaspoon.
I would probably use a large drill bit, a just drill holes in a grid pattern
to the correct depth and vacuum out the results. If doing this causes the
blocks to shift, then they need to be relaid anyway.

Christian.