At the time Dave A suggested this looked good for an Eastern Subalpine Warbler because it was so grey & cold looking but we didn't know of any diagnostic features. I've not seen the recent BB article yet but there was a short post on Birding Frontiers recently from Martin Garner pointing out Eastern birds have a different tail pattern - a white wedge on the second outer most tail feather rather than a white spot.
Have a look here: http://birdingfrontiers.com/2013/11/06/the-eastern-subalpine-warbler-at-yell/
Fortunately I hadn't deleted all my rubbish photos of the Skomer bird yet & found one that showed the tail pattern - is that enough of a wedge?
I left Pembrokeshire in August & meant to write a short goodbye post but never got around to it. I loved the time I spent on Skomer & really enjoyed the birding & meeting Pembs birders & hopefully I'll get back & do a bit more birding on the mainland. One of my favourite memories was bumping into a Red-breasted Flycatcher down North Valley & phoning Richard Dobbins when it had disappeared into a bush. While talking on the phone it popped out again so I put the phone down & watched it again for a few minutes until it disappeared again then picked my phone up & Richard was still talking!
Looks like I'll never get the hang of getting the photos where I want them & I've done something funny with the text now as well!