I came in on an an evisa, no problems. I don't why people would warn you away from them. The only thing I would suggest is that you bring a copy of the evisa with you boarding the plane and anytime you go to immigration, if you stay that long.
I am quite sure I can apply for an evisa in any country that uses the eVisa system, regardless of my current country .
If the Embassy grants the visa is another matter. I suspect this will vary by embassy, just like the hard-copy visa. Australia very easy, short lines, turn-around same day. Sri Lanka, very difficult huge wait, takes a week.
I have no advice for you my friend, but you're not totally in the wrong place. This is a pretty good 'everything else' page. Good luck to you, welcome to Thailand.
We had a group member said that he was from the US, applied for Thai visa while in Turkey. I was under the impression you can apply for evisa anywhere. It not like they're checking your location.
If you do decide to try for eVisa from the UK, let us know how it works out.