So I sent a mirror on a pole up the tree in order for me to monitor the contents of the nest. They laid 4 eggs, all hatched and this week were due to fledge. The only way for me to get at them to ring was to monitor them carefully and check the nest & tree each day for fledged youngsters.
The first two fledged today and branched to a nearby tree - allowing me to climb it and retrieve one of the birds (the other was too high up the tree!).
After ringing and a quick photo shoot, he was placed back in the tree.