Right you clever lot :D 

Does anyone know of a diagram that I can use to reproduce the "rope balls on a rope" often used for training purposes?

I seem to be able to get quite close but cannot get them exactly

Do you mean you want to make a rope ball tuggy ?

This site has pictures of what you are talking about

I think I have found it - all I need to do now is make a monkeys fist of it!

Are you having a conversation with yourself Kerioak.  They are only a couple of quid from the shows, life is too short to make your own :D :D

Hi Christine,

You can create a ball from a Turks Head as well as a Monkeys Fist.  Maybe this website will be of help to you.
http://www.folsoms.net/knots/turkshead.htm and http://www.folsoms.net/knots/thsamples.htm

Good luck and have fun!

Here's the Monkeys Fist.  http://www.igkt.net/beginners/monkeys-fist.html