Thanks to all for your advice.

I won't be able to commence this project for a few weeks yet so am
trying to glean as much information as I can first. I fitted my kitchen
last year and that went reasonable well but I did thoroughly research
how to do it first before starting.

The laminate I was going to lay says PERGO on the back and was
previously used in the kitchen, where it seem to cause no problem.
However, it was never properly sealed around the edges leaving the
'expansion gap' i think its called, exposed. Presumably this is why
damp got underneath the polythene or whatever it is you are supposed to
lay.

I think it will probably be ok for the bathroom [unless anyone strongly
thinks otherwise] as it seems like good quality stuff. I plan a trip to
the local DIY store to check if they still sell it and find the
specifications of what it is intended for