if your headlights go out when you push the start button, then i don't think it's a uk bike, as theirs don't do that.
the feed to the start button is from the headlight circuit on the US bikes, on the EU bikes it's fed from the IGN circuit (the same circuit that feeds the kill switch). if the bike is indeed a euro bike, and the kill switch works (ie the pump primes, FI lamp comes on for a few seconds), then there should be power to the start button. if the bikee is a US bike and the headlights work, then there is also power to the start button.
what i'd suggest is a simple test.
find the plug for the kill switch housing. using a wire or paperclip, short between the white/black wire and yellow/red wire on the harness side of the connector. that should operate the starter motor. if it doesn't then the problem lies elsewhere.
edit: i see you never checked any of the fuses in the fuse box. only the FI fuse and the main fuse. it's pretty certain that you blew a fuse in the fusebox (under the left side plastic by the coolant bottle)
check there and your problem is probably obvious.