On an emergency ceiling downlighter is a small green diode. This downlighter is in a highly rated lodge bedroom for members of the justice. The light stays on all night and the resident complains. Can the diode be covered? I personally think not! As it indicates whether the battery is charged. However, if you can’t cover the diode…… where does it state legally you can’t. 
Is there a similar product that does not have an annoying diode?

thanking you in advance. 

No, the "mains on" LED is an integral part of the fittings. I have heard anecdotally some of the downlighter versions can have it disabled but can't confirm this.

It's up to the Responsible Person to decide if they want to obscure this as they are legally liable - it has been argued that as long as the required monthly and annual testing regime is in place this would suffice - some places have increased the function testing to weekly as mitigation. Any deviation would need to be justified in the premises Fire Risk Assessment as to why it doesn't prejudice the safety of relevant persons.