Rhona I am so so sorry to hear about poor Fudge. It may be that his time for being called to the bridge is near. He is quite an old gentleman now and he is probably tired and letting his body become peaceful and ready for its last journey. He may look awful to you but inside he will be warm and drifting as his system lets go.
I have sat up at night with many a precious little one and seen them go and I personally feel that when I know the time has come, and you will know, it is best to allow them to pass gently in the warmth and security of their own little nest watched over by a loving owner. He will feel your love and it will be easy for him. Being boxed and taken to the vet will be traumatic I feel. If you feel able to maybe you could give him a little time to see if he can manage to go without pain. If you think he is in any pain then a trip may be needed and if the vet can do nothing, then the greatest gift you can give him is peaceful rest.
Hugs to you both and my thoughts are with you