Thanks for responses.
We were over broken cloud throughout except for about 5 mins complete cover. That must have coincided with coasting out as I never saw ocean below. Some heavier cloud cover and presence of the odd lenticular formation is consistent with a proximity to Snowdonia though.
Mil airspace over the borders tallies with my 'feel' for where we were, presumably keeping east of the Brecon/Knighton/Wrexham airway (Amber25 in my spotting days).