Thanks Pam and Kate.
I've had a look at the roots and they seem healthy enough. I'm sure if I went back to the supplier they will say it's something I've done (which it probably is).
I did repot them and at first they were fine, but it seems to be a gradual process. I'm not one to overwater so I'm perplexed as to why it's happening. I'll just have to do my best to try and save them.
Yes, it is Celia Smedley Pam. Don't know why I put Alice. I must have been having a brain block.