I don't think you will get it in a proper GPS unit, but there are a couple of add-on software packages for PDA systems (and notebooks):

http://www.memory-map.co.uk/

and

http://www.fugawi.com/

The main disadvantage is that the Landranger maps are raster and cannot be used for proper route planning, but as you know they are detailed and very nice to use.

Gareth