Luckily, a quick scan of the main pit revealed it as still present but typically at the far (and most inaccessible!) end. Using the anglers carpark I trudged to the end and was lucky enough to be able to get reasonably close. The bird was in a small group of Canadas as yesterday and easily picked out on size alone.
The following are my best attempts at getting it on film.
To my eye the most obvious differences between it and it's chums is the smaller size, smaller bill, thinner and shorter neck, slightly darker breast, darker flanks and the buff-toned and slightly narrower face/chin patch. The bird apprears to be a 1st winter.
After much reading I feel the bird is probably closer to the race 'parvipes' than 'hutchinsii' but I'd be very grateful for any thoughts or comments anyone has.
Having said all that the kindest thing that can probably be said of it is it's of 'unknown origin'!
Other than that I managed to add another 15 species to my Patchwork Challenge list bringing it up to a round 50 in 2 visits. It's all go here!