@BigJenny
Paddyk's link has this, rather pointed, piece of advice
"It can be tempting to try to ‘rescue’ a baby bird apparently in trouble. Here are some things to remember:
•The adult birds are much more skilled at looking after their offspring than humans will ever be!
•It’s very likely that the bird’s parents are nearby, waiting for you to leave the area."
(my emphasis)
Personally, I scatter dried mealworms on the grassy areas and blackbirds hop to and fro, gathering them up. I would suggest trying this as a bag would be only £3 (likely less than the price of a round trip drive to a wildlife rescue centre) and, if it succeeds in drawing out the parent birds from their hiding places, at least you know the fledgeling is still being supported.
Don't worry, if not. It may just mean the parents are onto their second brood. Then again, I saw first juveniles, of this year, over two months ago and have already seen one in adult black feathers but with a brown, not yellow, beak so, if this incident is recent, it may be a second brood youngster.