One point with the third brake light is that if it is obscured by a suitcase on the luggage rack it is regarded as not working. Although the third light is not a legal requirement, if you have one it must be working.
Some people remove them - but I didn't like the idea of being in a low car with a foreign lorry driver behind me - anything that would improve their chance of seeing me was welcomed!
When I had my Roadster I made up a light that would then fit on the suitcase - total cost was about forty quid.
Quentin
Why would you be more worried about a foreign lorry driver behind you than a UK driver?