There's two points here - use of red diesel and operator licensing - and they have nothing to do with each other except that when you take the 12,000 pages of tax legislation and overlay it with Defra's liking for complexity and all the fun of operator licensing you're going to produce authentic frontier gibberish which no-one can understand.
In Jan 2008 HMRC published the results of a year's work with the NFU etc working out which of the things that people did with tractors could be done using red diesel. They came up with a Memorandum of Agreement which is how the various pieces of legislation should be interpreted by HMRC or the old Bill when you get pulled over.
See
http://customs.hmrc.gov.uk/channelsPortalWebApp/channelsPortalWebApp.portal?_nfpb=true&_pageLabel=pageExcise_ShowContent&propertyType=document&id=HMCE_CL_000164#P36_1845 for the whole shebang, in particular the Appendix in section 10 for the Memorandum of Agreement.
Cutting to the chase you can take animals to market using red diesel but you can't then transport them once sold unless you use taxed fuel. The relevant bit says
QUOTE
Movement of produce and livestock
Transportation of agricultural, horticultural or forestry produce within or between different areas of land occupied by the same person.
Transportation of livestock within or between different areas of land occupied by the same person.
Transport of agricultural, horticultural or forestry produce from the place of production or temporary storage.
Transport of livestock to a place where the produce is to be sold or slaughtered.
The transportation of produce must be incidental to an agricultural, horticultural or forestry operation being performed on the land. The onus is on the person transporting the load to demonstrate that this is the case.
Transportation of produce which requires an Operator’s Licence may not be accepted as being incidental.
Transportation on public roads of produce or livestock by a contractor employed solely for that purpose is not included within this agreement.
UNQUOTE
The issue of tachographs is entirely separate and falls under operator licensing legislation. On which point it is technically possible for a Range Rover or Toyota Landcruiser to need a tacho in very extreme circumstances when towing for profit but that's because of their ludicrous weight. I don't think any of the Land Rovers is quite heavy enough yet.
