Thanks Gary,

All good ideas. I'm in London which is not humid, although unusually warm at the moment. I had this same problem a few weeks ago when things were decidedly colder.

I've got a sheet drying now and will ensure that it is totally dry before attempting to print.

I suspect Shanghai film might be the weak link in the chain. I use it because it is lovely and cheap. Possibly to my detriment, I had a happy accident with one of my first uses and got a great result. Without that accident I might have moved to a more resilient film some time ago.

I'll let you know the outcome of the test.