Many thanks for getting back.
So...all you require to be BS compliant is a "standard method of isolating the supply to each fitting (to simulate or induce a power fail)" which ideally would probably be a key-switch located next to the normal light switch feeding every maintained EL,
...or in my case, it could be the switch fuse feeding the lighting circuit. Both perform the task of dropping the supply and testing the EL.
As always Legislation / BS are open to interpretation, never a definitive answer!
Thanks again Tom, much appreciated