Hello Springtime: On the last trip out to the chalet, heard some high pitched urgent peeping on the stairs on the way up to the front door. The peeping continued, so traced the source to our small metal post box, still in the name of the previous owners. The post slot is very narrow, so could only just glimpse the top edge of a birds nest. Then realised that a rather anxious Great Tit was hovering on a nearby bush watching what was going on, squirmy inch long caterpillar in beak. Couldn't initially see any of the babies due to the angle and narrowness of the gap, but iPhone acts as a useful slim eye. Then obviously scarpered quickly so Mum's anxiety could subside.
There seem to be 6 babies, all very bossy and beaky.