Upperdeckpsr,
A casual glance at your posting is enough to realise that what BA are referring to is EXISTING collective agreements. MF would be a pointless exercise if all those on new contracts were then able to claim all the existing agreements currently enjoyed by cabin crew.
The reference to collective agreements which may be notified in future in fact allows the possibility that having agreed union representation these may well be applied. Obviously until sufficient numbers of the new crew decide who they want to represent them, this isn't going to be possible.
As has already been mentioned, all UK employees have the right to join a union and if enough join, collective bargaining becomes not a 'gift' of the employer but a statutory right. That union could be Unite, equally if the PCCC gain enough membership of MF they could form a union and gain collective bargaining rights for MF. As has been mentioned already, they are not currently a union but are following the procedures required should they choose to become one.