Thank you Mike, the call was louder and not as high pitched as I would have expected from a Crest, so this remains a mystery. Not so much of a mystery in the afternoon, when I had good views of a Honey Buzzard in very inclement weather flying west from the Williton area, over the garden. It was heading for a hedgerow in the field where there were a number of bee hives. It later came back and gained height and eventually disappeared out of sight.

Firecrest is the more likely option, they have a similar call to your description. No YBW reported since start of May & first arrivals were Sept last year.

Walking around my West Somerset garden at 7.30 a.m. this morning I heard a bird calling from the hedge. It was not the call of the local Chiffchaff but a more shrill ” Seeep “, which I identified as that of a Yellow Browed Warbler. I eventually set eyes on the small rather dumpy phylloscopus in the low branches of an oak tree and could make out the eye stripe. It was right beside one of my netting sites, but conditions were too windy to operate the net. This seems an unusually early date for this species ?