Neo - welcome to "our" forum.
It is great to see that you are so inspired about flying and are willing to join the fight with us, good on you.
The City Uni is a great place to start as it will give you an idea about being tested for colour vision. Just be aware that they are doing their own tests for their own purposes and they are NOT the same as the tests at the CAA.
The CAA will ONLY accept their own tests and will NOT take into consideration anyone elses examinations. (maybe other JAA aviation authorities as you will have read in this thead).
A word of caution about medicals. The first medical you do with the CAA is considered your "initial" and is more strict than others - it also includes colour vision which others do not. If you fail an initial medical, as far as I am aware (correct me if I'm wrong please) you cannot take another initial anyware in JAA land and will therefore exclude you from an unrestricted JAA medical if you pass the CV tests in another country. Please note this is the way I UNDERSTAND it - I hope others will give their informative comments on this. However the CAA will do only the colour vision tests for £28 - a good chance to do the lanterns, and if you fail at Gatwick and then pass in another country all is not lost.
As for the FAA route - you stand a GOOD chance of getting an unrestricted medical there. They have a lot of methods pf CV testing and the Light Signal test has a very good pass rate (me included). You need a restricted FAA medical to apply for the signal test, which can be taken anytime in your (FAA) training. As for working in the USA after, well as you are aware it is VERY difficult. My daughter is a US citizen (an lives there) and I cannot live or work in the USA. However there IS work on an FAA licence. See below.
1) There is a new registration M for Manx in the Isle of Man which comes under the CAA, but will allow FAA licences. It is NOT for public transport though - mainly business jets etc, but I think we will see a LOT more of this one.
2) The FAA licence is well thought of in Africa and the Middle East - if you want to work abroad.
3) Maybe you could get work on an N reg aircraft in the UK (don't hold your breath though)
4) Look at the USA as your training ground - not for work. I did my PPL in the USA and loved it - will be going back ASAP to do my CPL, IR, Multi etc.
In short - if you are willing and deternined enough, there IS work and you WILL make it on an FAA licence. Lets face it even with an unrestricted CAA medical and brand new CPL IR, you will have to be committed to getting a job in the UK - it will not fall into your lap!!
Good luck to you mate. Why not get flying. Go to a school you feel happy with and take a few lessons (you do NOT need a medical at this point) and just get "into it"