I may have posted this in the wrong place but as the insect in question was close to a river I thought it may be aquatic-related.
The insect was one of a happy pair on the shade side of a warm lichen covered wall at the side of the river Wye in Herefordshire UK. The joints and wrapped wing parts were really quite shiny where the sun caught, and the insect had two tails and two feelers - overall length possibly about 35 to 40mm. They were moving about perhaps searching for something but going back into crevices.
Thanks for that. Yes it looks like a stonefly but looking at googled images I cant see anything just like this (Perlodidae). The wings look too short. Perhaps it's just at the pre-adult stage and the wings aren't fully opened. I've submitted a large photo (use full magnification) to get a good view of its parts for better ID. The insects were at least 3m above the river level so perhaps preparing for flight? Also looked at: