Had a very speedy and friendly response from Peter in Warco spares. He said he was unable to check as current machines don't have a light but from memory they were 24 volt. He later asked around and concensus was they were 24V 2.2W. Size is BC9 so 9mm diameter bayonet cap.
Not easy to find but finally found some on Easy Light Bulbs site so ordered a couple.
Hadn't realised there were so many diffferent types, sizes, wattaage, volts, must be thousands of combinations, not the type you are likely to find on screwfix et al sites, not even Amazon turned anything up.
Fingers crossed for when they arrive.
Bill D.