It is Lynne's birthday and to celebrate George has taken her away. George knows it is his wife's birthday but he has no idea how old she is. This may be for two reasons: one is that Lynne has been lying about her age for some time now. Usually she tells people she is 27 and George has become so confused that he has literally lost count of her age. Either that or he frankly doesn't know, or care for that matter, and humours Lynne even though he is asking a legitimate question about her age. Due to Lynne's incessant lying, this puts her age somewhere in the mid to late 30s.
Not content with being taken to a hotel with a fancy venetian blind, Lynne gives a back handed stab at George's generosity by bad mouthing his choice of Champagne. If Lynne truly knew about Champagne she would have noticed it was Cava at the first sip and instead of using the word Champagne she would have said something similar to "Cava? It's my birthday and all you can get is Cava!" This shows that Lynne is a little nouveau-riche and does not understand the finer points of life, although she claims she does.
George is trying to coin a new phrase at the end but frankly it's not going to catch on. It's not often that men will be trying to save money on a costly weekend and be confronted about it. He shouldn't really reveal that he's trying to save money, but he needs to let Lynne know that these weekends away are hitting them hard and they need to stop. It's surprising that he doesn't let rip at Lynne, telling her that the Champagne is fine and it's her working class tastebuds that are wrong. But George isn't like that.