Godf
It could be any of the above suggestions, it is possible for an underground joint to be affected by water,
I would spend 40 or 50quid getting a sparky out to look over your fuse board and supply,
He would then tell you if there's a problem with your supply or there might be more that one problem,
(He might recommend a full test (PIR))
He could fix any lose connections in the fuse board/supply
(which is my guess at the min, but its only a guess)
before they get any worse and cause more damage!
Now might be a good time to find a sparky ready for your new kitchen work.