there used to be a spread betting company that offered automated trading: futuresbetting.com. unfortunately they are out of business since march, so at the moment you´d have to use a "real broker".
A good way to get started with automated trading is through a platform called Collective2 (http://www.collective2.com), which lists many systems for equities, forex, etc., which can automatically link to your brokerage account. This is particularly useful since you can launch a simulation account to give an auto-system a try without risking money.
I've spent a lot of time testing automated systems. Finally I had to conclude that watching the screen was about 10x more effective. I've only looked at the index futures in that regard. Going into relatively undiscovered territories like spread betting may be a good thing to do.
Good luck and happy trading.. I would check with all the brokers that offer what you want and ask about an API. If they can't talk intelligently about it they don't have it