I don't know for sure, but I hear great things about Tortose and Hare (Cranleigh) and another one in Farnham (can't remember what it's called). If you do get anywhere with these or others, I'd appreciate you coming back here and letting me know.
TE- Fair point. I was simplifying for ease of understanding. They encourage elements of good technique (Swim Smooth this is), but are VERY strong on improving your natural style.
The open arm stroke and higher stroke rate are generally not taught for pool swimming, though of course, an instructor with triathlon experience may be different. Both of these aspects are rare in good pool swimmers, yet are found in almost all good open water swimmers.
Ok, I'm bowing out too. Just go to the Swim Smooth website and spend an hour or two there. It's really good, has plenty of info and videos to explain what I'm trying to relay.
Dave- you say it's rubbish, but it's just the names somebody has light hartedly given to the styles of swimming.
The issue with a pool coach, is they will teach a pool stroke, which will not work nearly as well in OW and the 'Swinger' style WILL work well. It's a little like teaching someone to ride a bike on a turbo trainer.