We have just had a 7 month old tom, who hasn't had much people interaction, he was kept upstairs with other cats, we are not sure of the best way to help him, he is very nervous, hasn't eaten or relieved himself in about 12 hours, do we leave him to come round a little in his own time, or do we encourage him, food hasn't worked

Trying to convince him to let you touch him without giving him a break, will just make things worse. Work gradually. Let him have time by himself, but make a point of putting the food down while he's watching you (to get him to associate you with getting food) and work up to trying to get him to come to the food while you're nearby.

I wouldn't try getting him to eat out of your hand. Some cats just refuse to be hand fed. I also suggest you not try petting him while he's eating. Since he's spent all his time just with other cats, it's likely he's had to compete for food. Any move you make toward him or his food while he's eating could be seen as aggression and he could attack.

Let him have time away from people. If he goes into another room, don't immediately follow. Just go about your day as normal, letting him see you and get used to you being around. Eventually he should realize that you're not a threat.

It might take awhile to get him to let you near enough to really pet him. He may never be a cuddly cat. If you go slow and steady, and keep an eye on his body language, you should get him to at least the point where you can pet him without objection.

If his ears go back, his rump goes up, his fur stands on end, or he starts acting nervous in any way, leave him alone for awhile. Most cats are fairly easy to read when they get agitated.

Is he fixed? If not, then I would suggest waiting until he trusts you more before doing so. Cats have long memories, and will hold a grudge. If he associates you with pain and the vet before he learns to trust you, then he may never do so.

Do you have any other cats? If so, then let him watch you interact with them. You should also keep an eye on how he interacts with them, especially any other males. He may be aggressive toward other cats (trying to assert his dominance over them).