My first post was removed so here goes again.
Priority Pass have some black Friday offers on which means you can get 25% off the Priority Pass which entitles the member to unlimited visits for 12 months for £194. There is also 13% TopCashback which would probably get you another £25odd of the price.
Alternatively there is also another pass that is £119 and gives you 10 free member visits per year which averages out at around £11 per visit, less with cashback which when you price up the cost of an alcoholic drink at the airport you've pretty much paid for your visit!
You can bring additional guests for £15 or just get another card which may work out more cost effective.
Normally you can get lounge entry from anything from about £15 up to £20odd per person or for free if you are lucky enough to fly business class.
I know American Express have a Platinum charge card which has a £450 fee which also gives you Priority Pass for 12 months for you and a guest, plus a range of other travel associated points and benefits although they have got less appealing than previously with many clauses added to their travel insurance for example, so if you are just after the lounge this could be good deal.