You need to have made a few more posts to be able to post pictures (the rule is to keep automated spammers away). But normally you would expect to have a tang which tapers a bit, so you need to drill a tapered hole in the handle. Start with it still on the lathe, and drill through a hollow centre if you can. Another good way is to drill the hole before turning it, and use the hole to centre the work!
Go nearly full depth with a hole one size narrower than tip of the tang. Then use a bigger drill, and go a little shallower - the aim being to make a tapered hole into which the tang will be a tight fit. Try it; twist the tool so the tang works as a reamer. When the tool fits by hand pressure but leaves a gap of 5-10 mm, hold the handle (with the ferrule and tool in place) and bash the back end of it down on the bench so the momentum of the tool forces it into the hole.
If this all fails and you end up with a loose fit, use epoxy resin; but there should be no need.
Very good instructions Andy, the only thing I do differently is I use a mallet and strike the end of the handle, instead of the bench bashing. I feel that I have more control that way, and you can 'feel' when your 'there'.