[milestinsley]

I use http://www.fastspring.com/. I too am UK based and this solution works nicely. They're US-based, but it means anyone with a credit card (US, UK or whatever) can pay for your software and FastSpring just wire the earnings to your UK account.

I find this to be a far better experience than PayPal, Google Checkout and some of the others. They have great support and a really nice, intuitive backend admin interface. I think their fee (which can be 5.9%+$0.95 or 8.9% flat) is well worth it.

It's certainly a good starting point, even if you then build a custom solution later.

Good luck with your venture.

EDIT: Spelling :P