Many thanks to you all for your suggestions and possible solutions. We are coming round to thinking that having used the steamer to strip the old paper we have caused problems with the cork - more likely to have degraded any sealer than left moisture in as it was well over a month before we repapered. We have removed one area of cork to have a look under and there are some mould spots there. We will now act on all the advice, prior to repapering, and let you know the final outcome. Again, many thanks for your most constructive help.