RPL has now published a statement about its land ownership and relationship to Sustrans (actually, RPL and Sustrans are entirely different charities). See here:
More interesting to the average RR member will be the new interactive maps, which show RPL’s land holdings around the country – and inter-connecting routes developed by our partners such as Sustrans and myriad local authorities.
These maps could prove useful to RR’s area organisers and walk organisers because they enable users to identify both publicly accessible lengths of old railway and non-railway connections (bridleways, river/canal paths, quiet lanes, etc.) which can be used to link them together.