Help identify bird from call on Dorset coast today

Bird with very loud call seen in Poole Park, Dorset, this afternoon.  It was up a bare tree overlooking the lagoon.  About the size of a blackbird but difficult to see.  It appeared to be grey with possible yellow underneath and a thin beak.  Possible crest on its head though not certain.

its call was a repeated single note with gaps of a couple of seconds in between.  Merlin ID could not recognise it despite it recording clearly.  I have the recording from Merlin but don’t know how to share it to this page.