What are the factors affecting the voiltage rating of a CFL or other
electronically-ballasted lamp ?

For some time, I've been trying to find a 110V circline lamp & holder
for a particular fitting. I'm in the UK, and even 240V circlines aren't
very common. The equipment has a 240-110V transformer that I didn't want
to rewire.

Eventually, I decided to try a 240V CFL - and it strikes and runs
perfectly (not sure whether it's running dimly or not, but it's bright
enough for the application).

Is this OK, or likely to be overstressing the ballast, by taking more
current for a given power than the 240V circuit would normally need ?

-adrian