(disclaimer, the last time I had to deal with these things was 11 years ago, in the states. And I don't know what your exact needs are) I see you didn't direct

(disclaimer, the last time I had to deal with these things was 11 years ago, in the states. And I don't know what your exact needs are) I see you didn't directly mention Sage, I've seen a number of sites using Sage Pay for their online billing, and they don't seem to require a merchant account. (though fees are probably higher than others)