The information you seek, together with a lot else of value on RNAV operations, can be found in the excellent publication by Vasa Babic of PPL/IR Europe entitled RNAV Training Manual. It's obtainable from the Flyer Shop (shop.flyer.co.uk) and I'd thoroughly recommend it.
Be aware though, that for privately-operated G-reg aeroplanes:
1) very, very few aeroplanes currently have an appropriately-worded AFM Supplement for the GPS permitting P-RNAV operations; and
2) even fewer of their pilots (if actually any at all) have the requisite Operator's Letter of Authorisation for P-RNAV operations as issued by the UK CAA.