As far as I know, all three programs accept UK writers without a problem, and you may be surprised how many of your readers come from the UK as well -- but also from the rest of the world.
Before you put a lot of effort into promotion and such, have you set up Analytics yet? This will let you know where your traffic is coming from, what keywords they use to get to you, and how long they stayed there. All of this will give you a few more metrics for measurement and fine-tuning. I know when I started with Analytics I was very surprised to see some of the countries where I had quite a few readers, as well as which keywords were getting the people who actually read the whole thing (i.e. time on site is 2-3 minutes rather than 15 seconds). It's yet another proof that intuition about what will work is, quite often, wrong. Once you're signed up for the various affiliate programs and have your Analytics and ads set, dive into some promotion and you may be surprised how fast it starts bringing in quality traffic.