Oh weird, I see it's not working. Never mind, it's under "About Us" then "Access / Concessions" (then right at the bottom 'cos the page is ALL about access with concessions only coming in really at the end).
Note to all - always just book concession seats. No one ever has time to check! I've done that for years now. People are too busy!
Wow, where to start? You seem to be saying you're not strictly entitled to the concession seats, so either your avatar is a filthy lie or you... well, sorry to say, aren't looking that great for someone who is younger than 65. Either way, I hope no one takes your advice, 'cos it's pretty damn classless to be taking a concession seat that's designed for someone who needs it, and there's only a £3 saving from a standard seat if you book now, so it's not like it's the difference between being able to afford a show at all or having to miss out all together (and if £3 really does make *that* much difference, please - for your own financial security - reconsider whether you need to be spending ~£40 on a theatre ticket at all).