British Juvenile Pigeon Found! Please Please Help!

[Anahita46]

Dear Sir or Madam,
I was walking back from the hospital when i saw a juvenile pigeon on the ground cowering in the corner of a building! I thought he may be injured so I approached it and it hopped away flapping its wings but could not fly. He made a real attempt to get away flapping his wings but just couldn't muster the strength to fly I think. Anyway, I put him in a box with some bread crumbs and my friend is watching him till I get away from work in about 5 hours. I called a couple of vet practices and the RSPCA who said to leave him outside because "juvenile pigeons live on the ground for 10 days prior to flying and if I just put him back he will fly away." The problem is that is is raining here terribly and is cold and the wind is howling and i can't just "put him back." Also, I am not sure if he is hurt. It seems logically, if it is true, that he is perhaps just living on the ground now only to fly away in a couple of days but I now don't know what to do.
Do I feed him? Heat him? Isolate him? Treat him as a pet? Put him back outside? I am a doctor working in the surgical unit so I have access to dropper and syringes which i am happy to use to try to feed him but do not want to ruin his chances of survival in the wild. Please, please advise me on what to do.
In summary, he is a juvenile pigeon I found cowering in the corner of a building in Scotland, UK in the pouring rain in the cold. He flaps his wings and try to get away (I didn't notice any hopping or injury but I can't say with confidence I really checked him over). What should I do? I do not have baby bird feed or anything, but I need to feed him and care for him if he needs it. Please help me, I am scheduled to pick him up in about 4-5 hours from my friends.
Thank you in advance.