I have something called a "cash card" through Wells Fargo, though I have no idea if they have banks in the U.K. It works like a credit card, but you deposit cash into your account like a pre-paid credit card. I think the only real difference between it and a checking account is that it doesn't go through as a "debit card", so if a certain transaction accepts only credit cards but not debit, it will still work.
The main thing you will need however is just your ATM debit card, because that's what you will use to access your checking account through ATMs abroad. You will want to check with your bank, and make sure that it can be used from most ATMs around the world (i.e. it will have to have one of the symbols mentioned above for Cirrus, etc., but your bank should give you the general thumbs up or thumbs down on it. I think if it's a typical checking account it should work at ATMs around the world).
That's really all you need, but agree it's good to have a couple of back-ups, i.e. a cash card or pre-paid credit card, some cash on hand, and some traveler's checks as well. That way, if you lose your wallet, including the cards, the cash and the traveler's checks, you can at least get some cash back on your traveler's checks (although, that'd be tricky without ID, not sure how that would works exactly!). The thing to do is make sure to send yourself an email with the numbers of each of the traveler's checks so if all else fails, at least you have those numbers, which equal cash. But, think positive on that and hope you don't need to use them, in which case you just cash them when you get back home and call it your "time to get a job" fund upon returning.