Thanks Ekko Star for your interest and help with my BD50 problem, unfortunately nothing I tried worked.
I contacted Panasonic and after several days I received a reply from them, which said "submit the product to your local Panasonic authorised service agent for inspection."
I contacted the service agent and was told that there would be a £43 handling fee and further charges if a repair was involved. As they also had a queue system, it could take a week or so before anyone got round to looking at the BD50.
I decided that under the circumstances, I should just cut my losses and buy a new machine.
I bought a BD80, (multi-region for standard discs only) for £174.
The BD50, which I purchased about 18 months ago from the same firm, cost me £370 (with a price match discount).
This model is now currently available with them at £149.95.