Is it a nestling? ie. does it have a large gape/bright (yellow?) surround to the beak? If so, it's probably dropped out of the nest (2nd brood if a swallow) or tried its maiden flight too soon.
If it looks fully developed/adult, it could have been stunned by flying into a window/wall. 50/50 chance that with rest it might survive.
If it's a nestling, the advice always is - leave it where it is and the parent bird will seek it out. Obviously a bit late for that now, but you acted with the best of intentions.
The only wild bird sanctuary that would accept it that I know of is up here (Haggisville). NOT a great help. Sorry. There must be one on the Wirral or Merkeyside somewhere. ??
Hope the little fellow makes it.