Life saving operation for Junior

Hi, so my lovely Junior has been in the wars, missing for 3 and a half weeks, he made it home, straight to the vets, given medication, 4 days later took him back as he was deteriorating, his tail was falling off and open wounds to his back end. His tail needs amputating, his backend needs surgery, he has maggots eating him from wounds caused by an attack. He will not survive without the operation on Thursday. I don't have the full amount, I was told £900 to £1000 for the operation and aftercare.