All warblers look the same

Can anyone identify this bird with unremarkable quite dark plumage, and thin bill, seen at the top of a tree, near a small lake, surrounded by farmland, in Cumbria, in early March. I would transcribe its call as “bubber-dee, bubber-dee, bubber-dare, ba-dub”, frequently repeated. Video attached may not be much use for visuals but someone might recognise the call (ignore the chaffinch singing over it, and apologies for the sudden ending as I had to move aside to let someone pass!)

  • A Dunnock is one of the most misidentified of the common birds and of course it is not a warbler. They are singing strongly at this time of year with their sweet although simple songs. Here's what one looks like in full voice.