Well, Wheelers just munched through my desk draw knobs and has now decided the corner of it is a great after meal nibble
What can I put on it so he wont munch any more of it? I've heard of bitter apple spray but Im not sure where to buy it?

Information greatly appreciated by me and the desk!!!

Bitter Apple any pet store, oil of cloves, vicks vaporub.......

Or try TCP or olbas oil!

Juice from chillies

Dont leave him in the room on his own, only have him in if you can watch him, and when he looks as if he is going to chew something say a firm no, if he still takes no notice go over to him pull him away and firmly say no, and keep doing it until he stops how ever long it takes, as soon as he stops reward him with food. Stay beside him and see what happens next, if he goes back to chewing again, go threw the whole proccess again. You may need to go threw this several times but it should sink in.
Also give him something he can chew, to satisfy that need.
My dogs have that need every day.
I hope this helps.

i found that oil of clove worked a real treat

Vicks vapour rub.  I tried everything but this stopped his chewing in its tracks.  We have now gone over three months with nothing.  They hate the smell and dont like the consistency of it and it stays smelly for ages.