For UK cars in the UK - "if a high-level brake light is fitted, then it must be visible"
-However there is no statutory requirement to have more than two lights - so remove it
Like so many things on cars; if it is present it must work, however the requirement for it to be present is a 'may' and not a 'must'.
For UK registered in France - at least until June, the same as above.
For French registered cars in France, I've no idea.
