Priority Pass is ideal for international travel, with its numerous independent lounges (sometimes airline-affiliated) worldwide. The amenities range from adequate to luxurious.
You mentioned LHR/LGW. At LGW there are 5 lounges to which you can gain entrance with PPass: Delta Airlines First & Business Class Lounge, Sir Ivor Broom Suite, Sir Robert Hardingham, Servisair Executive Lounge, The Alexandra Suite.
At LHR there are 6 PPass affiliated lounges: KLM Executive Lounge, Kuwait Airways Oasis Lounge, Servisair Executive (3 locations), The Business Centre.
There also happen to be two lounges at BAH (Gulf Air and Delmon), and one (Gulf Air) at DOH.
I have personally been at none of the above, so others would be more apt to provide first-hand experiences with them. But these are the lounges listed in the directory in the airports of interest. However, having been to other PPass-affiliated lounges in varous parts of the world, I have developed the opinion as mentioned above about the faciliaties in general ranging from adequate to excellent.
You obviously have web access, so you can check out the PPass website at
www.prioritypass.com (I don't think this one would be censored in KSA) for membership details on the program.
As for Diners Club, I would suggest using it more as the charge card it is, and rely on a PPass (or airline affiliated) membership than for lounge entrance. As you will see, the number of lounges affiliated with Diners Club is relatively few. However, the annual fee (at least in the USA) is about a third- to a quarter- that of PPass membership. Furthermore, the membership (and any fees for guests) can be charged to DC, earning the mileage credits mentioned above.
Each membership is non-transferable, so unless you are travelling together to get each other in as primary/guests, an individual membership would be needed for each of you.
Keep in mind, too, that membership to airline-affiliated lounges does not necessarily require FF status. Memberships are usually purchased independently, and in fact are usually run as separate business units by the airlines themselves. However, by going the airline-affiliated route, do keep in mind you may be limited to only however few or many lounges within that club's network, and their use may be restricted to only when you are travelling on their ticket, whether codeshare (such as Star Alliance) or not. As I said, PPass is ideal for international travellers.
Take a look, and let us know what you think or if you have any further concerns or questions.
Good luck.
[This message has been edited by FQTV (edited 07-15-2000).]