I recently moved into a house that has a decent sized understairs
cupboard. It has no power (although it does have a length of T&E
powering the alarm system, there is about 5 feet of cable on show which
appears from the floor above) and I would like to put a light in there.

Is it possible to DIY it? I have a spare 3m length of LED lights.
Perhaps I could put a socket in the line before the alarm. I can't tell
where the power for the alarm comes from, the CU does not have a
designated line.

Any thoughts?

Thanks
Mark.