Neil, this is a regular Topic question on the Forum across several models not just Lacetti. There can be various reasons.
Often all that is necessary is 're-synchronisation'.
The Forum Advanced Search function will provide the previous discussions. I've provided the link which you can read the various issues here:- Search results for query: central Locking not working
It is usual when Signing up to complete your World location (Forum system believes you to be in UK ?) and vehicle details go in the designated section. Other helpful reading on the following link:-
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