Dean - what you will find really annoying is that, up to a couple of years ago, Plat Amex holders got access to Virgin lounges even when flying economy. This was a fantastic perk that was pulled due to overuse, I believe.

The best perk in the UK / France is actually the use of the Eurostar lounges. Even some business class Eurostar tickets do not come with lounge access, so being able to walk in on a £59 economy ticket is fantastic. They are lovely lounges as well, post the Phillip Stark revamp.