AH64...
There is
no VIP "system" in BA... As a new entrant, plan on being rostered every weekend outside leave, and you won't go far wrong.
What n_n is referring to is a system whereby for strong compassionate reasons you may be "let" off a duty you were rostered for. Strong reasons are just that. NB to BA, something as trivial as your own wedding day should be arranged to coincide with your leave etc.
Of course, there are all sorts of namby pamby euro / New labour laws which can get you time off - Parental Leave, Dependant's days etc. which they cannot deny.
In summary:
Ta for that - is there any sort of VIP system for booking specific dates off - e.g. wedding anniversary?
no - and something like that would not be regarded as anything like strong enough to use the system n_n refers to...
HTH
NoD