I've just had a conversation with BA on Twitter about this. Apparently, entry to No. 1 Traveller lounge is offered "as long as capacity allows". Given that the Club lounge at Gatwick was about the same size as the No. 1 Traveller lounge and now all BA's passengers have to fit in there also I suspect this is going to be a significant issue. I can see a situation whereby Club World / First passengers who've paid thousands for tickets are turned away at the door.
Next I asked about what was included in the lounge. Apparently, champagne is not complimentary whereas it is in the BA lounge. I think this is a really poor show by BA. They could easily have ensured that production of an eligible boarding pass (status or passenger in Premium cabin) could have had ensured access to complimentary champagne. This all smacks of cheapness by BA. I've got three tickets in Club World in April and suddenly we're not guaranteed lounge access and there's no complimentary champagne if we do manage to.
Yes - it's a first world problem - but if you've paid for something I really think you should receive it.