Hi there,
This is indeed a juvenile Robin, as suggested by all who responded.
For future reference, even though the actual size is not apparent in the images alone, Robins have very different proportions to Blackbirds, and it is fairly evident on the shape alone that we are not dealing with that species: the head, in particular, is disproportionally large when compared to that of the Turdus thrushes.
Juvenile Redstart would still have an orange tail, though this can be harder to see when closed, as the central pair (visible from above on the folded tail) are often darker. It would also differ structurally from the subject bird, as would juvenile Nightingale, and, rather helpfully, the juvenile Robin in your pics already appears to be attaining some hint of the orange face and breast found on older birds, a feature that would not be shown by any other juvenile chat in the region...some species would attain orange feathers on the breast, but not on the face also.