Going through pictures taken back in June in Scotland I took a much closer look at these 2 of a very grey and dull Willow Warbler that was singing it's heart out in scrub by the Cairngorm carpark.
This individual shows characteristics of 'Northern' Willow Warbler just taking a quick look at the Collins guide. I started digging a little deeper and found this interesting blog article by Mark Lewis
I won't repeat anything he's so eloquently written but from what Mark is saying it would seems that this bird is probably an 'acredula' bird which may be more common in Scotland than we previously thought. It's certainly very different indeed to the green and yellow 'southern' birds of the 'trochilus' race we're used to in Norfolk!