I have put some new taps in the bathroom sink and need to wire them in. The old tap had a red wire and also a red and black coloured one. The new tap has a white wire and also a white and black coloured wire. Am i correct in thinking that the white and black wire will go to the red and black wire and the plain white one will go to the red wire ?
I take it you mean that the one wire is plain and the other striped. The striped one should be the positive and the plain the negative so yes you are right that they should go in that order, striped to striped and plain to plain. Make sure that you cover any visible copper cable with insulation tape otherwise you will likely to blow a fuse especially in damp areas such as the kitchen or washroom. I haven't see a caravan with a bathroom...lol.
Technically, the switches don't care about polarity as they are only switching one conductor of the supply, but best to try and keep to an established wiring colour scheme if at all possible.
I rewired my shower taps and rehoused them in a wall-mounted ABS box last evening:
The original wiring was purple and purple/black, I just used 2 colours off the wire rack.
The switches drive a 30A car relay which takes all the pump motor loading, the microswitches last a lot longer that way.