When holding the violin bow should the knuckle of the thumb be in contact with the bow or totally free of it? Sorry for the basics of this but I can't remember the correct way and when I look in manuals they don't seem to make this clear. Any advice welcome.

The thumb must be bent and the knuckle does not touch the bow as a result.
There is no definitive right or wrong way but this way produces best results.

Thanks V.H. I do find though that even when I start off in this way my knuckle starts to support the bow without my consent as it feels more comfortable and secure. Does it make such a difference? Should I nip it in the already flowering bud?

Knuckle should not rest on bow as it makes lots of the hand muscles tense and then it is harder to make a nice clean sound.

Yeah try and stop resting knuckles on bow. No knuckles should touch the bow. Check with your teacher though. My teacher had a go at me for bow hold at my lesson yesterday. My thumb was not bending at all!

Oh well, hope you can correct it, it will take time.

Hi V.H. I don't have a teacher so I just dredge up as much as I can that they taught me in my younger days. It's not ideal because teachers constantly check that you are not developing bad habits which you're not always aware of until it's too late. Anyway practise went well today with no problems - I really just needed reassuring which was the right way. I just got a blank about it. Thanks again.

This is good advice, but I would just add that the thumb doesn't have to be very bent at all (thus resolving the contact issue). The important thing to remember is that it should not be rigidly flexed - if it is, it will impair your playing and tone production.

Try thinking about keeping your thumb round and flexible, rather than rigidly bent into a square. Think of grabbing hold of a water bottle (one of the narrower ones) and pouring the water out - your thumb will be round the bottle, and, with a bit of luck, curving round and well behind your first finger.
Hope this helps.

Yes, that's a good visualisation. I'll give it a go. Cheers!

You can always put anything you like in the bottle !!!!!!

Erm, despite what people are saying it's actually fine for the thumb to rest slightly on the bowhair by the frog. It depends on your bowhold/style, hand size, arm length, and where abouts in the bow you are. Saying your thumb must not touch often leads to a locked thumb. Your thumb should be free enough that if it wants to touch the hair it can. I would challenge anyone to perform string crossings on G+D strings using just the inch of hair nearest the frog without their thumb coming into contact with the bow.
If you feel more comfortable with your knuckle on the bow then go for it. Ask someone who can actually see your bowhold to advise you. The most important thing is that you are not putting tension into your right hand and you should seek to achieve this however necessary.

Mine touches the bow hair slightly and it's really uncomfortable for it not to. I have to really force my hand not to touch the bow hair and resultantly can barely move my hand/wrist/bow! So i just leave it as it is with it touching the bow hair slightly and my teacher said my bow hold is fine