Little Bunting

Wing shape comparison (Little Bunting on top)

Tail feather comparison with Reed Bunting

Beak Shape Comparison with Reed Bunting (Little Bunting to left)

Flank comparison

Little Bunting, Dunkirk, 6th October 2013 © Tony Martin
'I had three reed buntings in a net this morning, and was struck by how small one of them was. Then I noticed that the beak of the small one didn't look quite right, and the head colouration was similarly unusual. And it had white on just the outermost tail feathers, unlike  in reed buntings. And the wing shape is different, and there's no emargination on the 6th primary. By the end of all this, I became convinced that this ain't a reed bunting.
I'm not altogether certain, but I rather think that this might be a Little Bunting.' TM
NOTE: ID since confirmed by Michael Holdsworth - Ed