Well, it's not a Finch type bill, there's no white shoulder bar and those would be very bright legs for a Chaffinch?
It's not a great match I admit!
The bill - It's a poor photo, and I think what is seen of the bill is mostly highlight, with a fair part of the substance lost in the haze, but I could be wrong.
The shoulder patch - It's a poor photo, and I suspect much of the shoulder patch is, as can be the case, being covered by mantle/scaps, but I could be wrong.
The legs - it's a poor photo, but what I can see of the leg looks like a brightly lit pinky Chaffinch colour, blending into a brightly lit yellowy green bud on the twig (one of several in this shot), but I could be wrong.
I'm pretty sure I see white edges to the tail and tertials, the hint of a pale (whitish?) patch at the base of the primaries, and a white vent, all problematic for Dunnock. But I could be wrong. It is, after all, a poor photo!
EDIT - Could even go for female Pied Fly, but it feels a little early, and shape and posture look a bit off. Dunno. Odd one.