Fredxxx wrote:
This is a 3-phase job where the control is non-latching and through a
contactor.

Does anyone have any experience with any make of transmitter and
receiver system which is secure?

Any suggestions?
You could try this lot http://www.garage-door-remotes.co.uk/

All depends on how secure you really need it. Any system can be broken
so should be thought of in terms of how long the bad guys will need to
get in compared with going round the back and going through the window
or similar.
If the contents are insured, then the insurance co may take a view on
the security needed.