Hello, fellow UK-er person (I assume, anyway!),
I jumped straight on the very first Discover More preapproval I got in the mail, last August. They're usually a TU puller (but sometimes go for EX, I believe), and mine was my highest at the time - 740-something, I think. Household income considerably less than yours. I got approved for a $4900 CL, but did have to call in first to verify my identity. If you do go for it and get some message about how you have to call them, I think that's basically because they've pretty much approved you but want to prove you are who you say you are by asking you a ton of questions.
Anyway... it's a pretty decent card, I'm very happy with mine. You're never going to earn a ton on the basic rewards (0.25% on the first $3000 per year, then 1% after that), but the quarterly 5% categories are nice to make $20 here and there, and the real $$$$ is to be made via ShopDiscover - basically if you ever plan to buy anything you can order online, check to see if you can get it from a ShopDiscover retailer (lots of high street stores etc on there), and if it's worth your while to do so. You can get a nice amount of cashback that way - so the card is good for earning money on "bigger" (even if they're not very big - just anything that merits being bought online, really!) purchases even if not on everyday run-of-the-mill stuff like gas, groceries and the like.
I'm pretty happy with them, all in all... nice customer service (once you convince them to stop trying to sell you stuff - just ask to be put on their "no marketing" list at the first opportunity you get, or you'll be forever fending off calls trying to flog you credit monitoring and payment protection and other stuff you don't want/need), reasonable - if not enormous - CLs, and they seem relatively sane and well-balanced compared to a lot of issuers out there right now.
If you're tempted, I'd say go for it!! 
@Anonymous wrote:Hello, fellow UK-er person (I assume, anyway!),
Ha, yes, indeed! London --> New York --> Dallas (I was meant to go home nearly 18 months ago but stupid falling in love... now it looks like I am here to stay, unless DH gives in and agrees to move to the UK for a short while before returning here)
I jumped straight on the very first Discover More preapproval I got in the mail, last August. They're usually a TU puller (but sometimes go for EX, I believe), and mine was my highest at the time - 740-something, I think. Household income considerably less than yours. I got approved for a $4900 CL, but did have to call in first to verify my identity. If you do go for it and get some message about how you have to call them, I think that's basically because they've pretty much approved you but want to prove you are who you say you are by asking you a ton of questions.
I was thinking about calling the number they gave me to do it, maybe that would bypass that step!
Anyway... it's a pretty decent card, I'm very happy with mine. You're never going to earn a ton on the basic rewards (0.25% on the first $3000 per year, then 1% after that), but the quarterly 5% categories are nice to make $20 here and there, and the real $$$$ is to be made via ShopDiscover - basically if you ever plan to buy anything you can order online, check to see if you can get it from a ShopDiscover retailer (lots of high street stores etc on there), and if it's worth your while to do so. You can get a nice amount of cashback that way - so the card is good for earning money on "bigger" (even if they're not very big - just anything that merits being bought online, really!) purchases even if not on everyday run-of-the-mill stuff like gas, groceries and the like.
I'm pretty happy with them, all in all... nice customer service (once you convince them to stop trying to sell you stuff - just ask to be put on their "no marketing" list at the first opportunity you get, or you'll be forever fending off calls trying to flog you credit monitoring and payment protection and other stuff you don't want/need), reasonable - if not enormous - CLs, and they seem relatively sane and well-balanced compared to a lot of issuers out there right now.
If you're tempted, I'd say go for it!!
Good to know, I don't really have any rewards cards at the moment so it would be nice to have one just to put all the monthly expenses on and then PIF to earn whatever I can... better than a kick in the teeth and all that. Thank you for the quick reply fellow UKer!