What is the best option to use for many, many D.Boards that have padlocks on as per picture.
The Disconnector is not accessible. Some I have seen install an external isolator clearly marked.
Some cut a hole in the DB front door. Some have a break glass box with a key for the lock.

The main switch-disconnector on each distribution board shall be easily
accessible. (See also 6.6.1.1(b), 6.6.1.1(c), 6.6.1.6 and 6.6.1.9.) If, owing to
the nature of the installation, it is necessary to be able to interrupt the supply
immediately, the switch-disconnector shall be so installed that it can be
rapidly identified and operated.

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