Well, you can paint it with Arbrex if you want to, but what's more important is that the cut is a clean one, with no snaggy ends and no split bark left on the main trunk.

Rub some moist earth into the clean cut.

I remember reading an article from the RHS some years back where they were saying Arbrex is not nessasary, carnt remember what they actually said but they were condeming the use of Arbrex.

Yep, I read the same thing, and I never use it, just make sure the cut is a cleanly done one.