We had a 'heat wave' last summer where it got into the 80s and 90s - but that is not the norm here. I pulled some data from weather.co.uk to get monthly averages:
The hottest months of June, July, August and September averages are:
June
Max: 19°C (~66F)
Min: 9°C (~48F)
July
Max: 22°C (~72F)
Min: 11°C (~52F)
August
Max: 21°C (~70F)
Min: 11°C (~52F)
September
Max: 19°C (~66F)
Min: 9°C (~48F)
Ambient temperatures (and humidity) make growing the cool/cold loving types ideal!
I will take your advice and not mount on of the two that I have (playing it safe!) and only put in new additions which are already going through an adjustment. I hope that by providing a welcoming environment, they will settle in well.
Regarding growing terrestrially - most are true epiphytes, however, apparently some of the species are found in the wild growing terrestrially. According to the Internet Orchid Species Photo Encyclopedia the following have been found as terrestrials:
IOSPE PHOTOS
IOSPE PHOTOS
IOSPE PHOTOS
..as well as the two I already mentioned, and a couple of others. Not that many, but enough to be a nice variation in a collection, I think!
Looking forward to this weekend and the Open Days at Ratcliffe Orchids (which is about 15 minutes away) - if only I were into Phaphs!