Andrew wrote:

My problem is that I have a problem with the wiring between a ceiling
lamp and the existing light switch on the wall on the opposite side of
the room.

The ceiling lamp has power but there is no continuity to the switch.

I want to install a wireless switch on the wall in the same place as
the existing switch and install a receiver at the lamp to switch the
lamp, rather than chase out and redecorate.

Firstly, how come the ceiling lamp has power? Surely the live
wire to it must go through that switch. In which case maybe the
switch is faulty and should be easily replaced. If there is a
problem with the wiring is it safe to leave it like that?

Secondly, if the wire needs replacing it may be possible pull a
new wire through by attaching it to the old wire.