Hi Alan,
The geographic areas across the UK as a whole are pretty much already covered by established 4x4 Response groups who have written Memorandums of Understanding with the appropriate Police Forces and Regional/Local Resilience Partnerships.
It's unlikely you will see any 4x4R group called out by anyone to recover vehicles; that's not what 4x4R was established for. On an odd occasion, if individual circumstances required it, a Responder might consider moving a vehicle by means of towing, or perhaps winching - if he or she has the correct training to do so - but that would be an exception to the norm, and is not something we are normally asked to do by the Police. The local recovery agencies on the Police callout lists would probably be none too impressed if we started doing their job for nothing too.
This page shows a bit more about the capabilities of groups, and what the user bodies expect of us as an organisation.
http://www.4x4response.info/?pid=groupcapabilities
Sorry if I sound a bit of a party-pooper, I don't mean to be; there are potentially very serious consequences if a 'volunteer recovery' goes wrong - even more so if someone is injured - and that is the primary reason Police Scotland - and others do not officially task us to undertake recovery work.
One thing you would definitely have to have in place before you started any discussions with either Police Scotland and/or the LRP/Council, would be a very comprehensive Public Liability Insurance Policy covering you specifically for any voluntary work you intended to undertake. I don't think you would be able to get cover to indemnify you for voluntary vehicle recovery, without producing huge amounts of supporting documentation around personal qualifications, health and safety procedures, risk assessments and so on...
However, if you were to join an established group, such as Lothian, you could become more involved in the activities they do get asked to do.
Hope this is useful.
Warren