Thanks Mohammed, for your reply, but it doesn't help me very much. No point you referring me to the Microsoft help on Bitlocker, (I have read it), this is a BUG. It is not due to me doing anything wrong. Bitlocker locked my drive without me requesting it. (Contrary to your assertion that Bitlocker only locks drives when requested).
I will post on the Tech forum as you suggest, but with no great hope of solution. This needs to be reported to the relevant operating system support team, and it should be solved by Microsoft, who should get back to me with their solution.
One final point. If I try to do a Dir on the drive in the command prompt it says:
"The bitlocker metadata for the encrypted drive is not valid", further indicating that some sort of system error has occurred. A question. Since the drive can still be viewed on the 8.1 machine, if I reformat it from that machine, will it then remove the corrupted bitlocker metadata?
Thank you