A lemon oil wipe is fine once in a while, Jazzy. I'm not sure if the product I use is available in the U.K., but probably an equivalent. I use Minwax finishing wax, a petroleum-based paste that is especially good for preserving bare wood.
When I do these in my shop, it's usually following planing the fingerboard to true it up and remove years of wear. I'll follow the planing with sanding, then ultra-fine wet-sanding, almost like a lacquer finish. A little buff, then wax. I started using it on the bare wood maple or beech necks years ago, and discovered that it really shines on dark wood fingerboards too.
