Hi Mike! Thanks for your reply Do you mean club together to upgrade their whole ticket to Business Class? If so, I did consider it, and will check the price, although it's almost certainly above our budget/finances. They are a friend of me and my wife (it's her 40th trip), but not close friends with our other two friends flying with us, so wouldn't be right to ask them to contribute.

As for paying just for the lounge for the fifth person, my understanding BA don't offer this. It's exclusively for Business/First and/or Silver/Gold level members.