On the Lloyds Premier Avios Amex* you earn a big 1.5 Avios per £1 spent on Amex. It comes with a Mastercard too, though only spend on Amex as it gives the most miles.
However, there's a huge £140 annual fee so be sure you'll use the rewards, otherwise you're just wasting cash.
If you reach £12,000 spend in a year, you'll get a
(you'll still need to pay taxes), which can be used when redeeming your Avios points. You can use it for Eurostar tickets too. If you don't think you'll spend that much or don't need the extra flight, it's not worth paying the fee.
Plus, if you spend £5,000/year you'll be sent a voucher for two flight upgrades, either for two single flights or one return journey (though, again, you still pay taxes).
Avios can be redeemed on BA and other Oneworld airlines, including American Airlines, Cathay Pacific and Qantas. See the Avios site for where you can go.
The APR on purchases is 18.94% (or 52.1%
APR including the annual fee).