Got a humming noise when I let of the accelerator but before touching the brakes, gets less noticeable if I put it in to neutral? Any ideas

Possibly front diff related. Fairly common issue, unfortunately...

Of course, it could be something fairly simple, such as a wheel bearing, they both have a similar rumble when failing

Thanks is there any way of diagnosing which one? If its front diff what needs to be replaced?

Jack up the front end, and check for any play in the wheel bearings, or any noise as you turn the wheel.

To diagnose the diff, ideally you need to drain the oil and check its condition. If it is a clear, brown colour then it is OK. If it is a black/grey colour, then its a good indication its a diff bearing breaking up...

If you lift off from about 60 or more e.g when coming off on a motorway junction, does it make a fairly loud 'wup, wup, wup.... noise a bit like the noise a flat tyre makes? Mine did that when the diff was on the way out. +1 for DM's comments about black silvery diff fluid and also lots of metal particles adhering to the magnetic drain plug.
New diffs are not available but Duckworth Parts will sell you an exchange LR reconditioned unit for £763 delivered. A good local Indie fitted mine for £350 so not cheap but could be worse. If you order a diff don't forget to order some correct diff oil at the same time
Diff comes in a big crate and looks like this:
 2008 MY Java Black TDV8 HSE