Yes, I agree with Alf.......... but, it does rather depend on what the specification actually was of course.
Apart from that, I have to say the builder's attitude is unforgivable. £10k is a lot of work for water damage. Any decent builder should expect to give a little thought to aftercare, especially with a job of that value. Even if it were a ten pound job, most customers are grateful for a little "hand-holding" in order to tie up any loose ends or problems. So many tend to think that a job is over the minute the cheque is handed over.
The insurance company should at least be kept informed, if only to protect you if more problems crop up later as a result of the work. You may even need to claim again!
To be practical, it's the worst time of year for anything to dry out. When the fabric of a building is water-logged, it can take ages. At a guess, I'd say the ceiling still has some drying to do. In the meantime it's presenting a cold, damp surface where condensation will easily develop. It could be as simple as that.
The light switch sounds like it's relevant. If it was damaged in the flood, it should be fixed.
Flooding wouldn't normally cause a WC to leak....... but, perhaps re-fitting it was part of the spec., in which case it should be done.