Please help me with this mystery warbler - I'm on holiday in Orkney

Saw this warbler picking off insects from a bush in the garden of a holiday cottage in Orkney.  It was largeish, and very noticeably VERY yellow underneath going right down the body, with only the hint of a supercilium.  The photographs were taken through a window, so the vividness of the colour has been bleached out a bit, but I didn't want to lighten/brighten the image for ID purposes.