BA A380 seat layout

If my memory serves me right (it may not!) some time ago, Virgin wanted to make the upper deck of the LGW/MAN 747's all Upper Class to free up more space on the main deck for more PE/Y seating. They fell foul - I think - of either the Disability Discrimination Act, or some CAA regulation that states that UK registered airlines have to offer all classes of service to all passengers. By having UC only upstairs (with no passenger lift) they could not fulfil this requirement.
I've just noticed that BA only offers World Traveller Plus (Premium Economy) on the upper deck of their A380 fleet. How did BA get round this rule? I appreciate the A380 can be boarded / disembarked on both levels - which should not be a problem for BA at LHR with T5. What happens if they fly to an airport and are not allocated a gate with dual level airbridges? I appreciate that the BA A380 fleet is a relatively small sub-fleet, so BA can probably manage to deploy it only on routes where the destination airport is suitably A380 ready with plenty of gates with dual level airbridges - but there will doubtless be occasions where they do not get allocated such a gate due to issues beyond their control (delays on other airlines flights that are blocking gates etc).
Or was the crux of the problem for Virgin that the upper deck exit door on the 747 is only designed / certified as an emergency exit - it cannot accept a jet-bridge as the door opens upwards? Just wondered.
I've just noticed that BA only offers World Traveller Plus (Premium Economy) on the upper deck of their A380 fleet. How did BA get round this rule? I appreciate the A380 can be boarded / disembarked on both levels - which should not be a problem for BA at LHR with T5. What happens if they fly to an airport and are not allocated a gate with dual level airbridges? I appreciate that the BA A380 fleet is a relatively small sub-fleet, so BA can probably manage to deploy it only on routes where the destination airport is suitably A380 ready with plenty of gates with dual level airbridges - but there will doubtless be occasions where they do not get allocated such a gate due to issues beyond their control (delays on other airlines flights that are blocking gates etc).
Or was the crux of the problem for Virgin that the upper deck exit door on the 747 is only designed / certified as an emergency exit - it cannot accept a jet-bridge as the door opens upwards? Just wondered.