Friend left dog in my care since July, won’t return calls or texts (England)

Good afternoon, I’ve seeking advice as a dog has been left in my care since July, I have been asking the owner to get the dog since August. I have contacted shelters and the police for advice but everyone is saying there’s nothing I can do without the owners permission, I contacted the local warden and he can they said they can’t do anything (lady on the phone sounded very young so I’m not sure how true it is) I’m left going round in circles as my friend orignally was going to pick him up after a few days but it’s been nothing but excuses and now won’t return my calls or texts. I’m at a loss of what to do and the dog is kept outside 24/7 due to not being house trained by the owner and I have my own pets to worry about and now the weather is getting really cold of a night I’m worried about him and he’s been crying at my back door most days. What can I do?