tingtang
let me answer some of your questions and give my two cents.
-Authorized course in the UK, for Atpl exam in the UK: YES, unless you have a bunch of multi-pilot commercial time (1500), which is not the case!
-After the ATPL papers, 36 months to complete UK CPL
AND Instrument, Yes
-You would need an Faa CPL not ATPL! big difference ( at least 1310 hours less)
-ATPL skill test
please buy or borrow a LASORS, you will get
all the answers, once you passed the 14 ATPL papers, passed (whichever way you want) the UK CPL, multi engine rating and instrument rating skill test, you hold a UK JAA Frozen ATPL!!
Last but not least, you want a JAA first class medical!!
-you will need either an initial examination at Gatwick or a JAA first class medical transfered from a Jaa country, like France or Germany (the requirements are the same:JAA!!!)
not a medical from the US, you were mislead or misunderstood.
If wannabee are advised to, first pass the first class medical before anything, it is because it is a mandatory stepping stone on your path to professional aviation.
On another hand, it is not unheard of, that high time experienced pilot sometime enjoy a little "favor" in view of their career.
Others before,(i have known a few), have been thought FAA licenses hoping to "arm-twist" the JAA regulation, only to find themselves either in big financial distress or flying in Africa or eastern Asia.
Do not misunderstand my words, i have nothing against flying in those place, to the contrary.
But your original goal is to fly in the UK, so you would be way off-route.
I hope you will get your first class medical ans that you will fulfill your dream.
Have a good flight and be safe.
P.S. how do i know? been there, done that.: