Do all new installs have to use EN54?

Does all newly installed equipment have to be EN54 compliant or can 'new old stock' equipment certified to BS5839 still be used?

Somebody I know asked an engineer this and he said that by complying with BS5839 you were automatically compliant with EN54 but I thought after he might be thinking more of the system design aspects rather than the certification of the equipment itself.

As  an example if I had a Kentec K3000 control panel and some Gent 1195 call points both of which are BS5839 could that be used for a new system as long as it was installed & tested correctly?

Thanks