Saw this…

…and thought of Chippy.  He had a Land Rover, converted for Camping, didn't look this big though.  I didn't get to see inside, but did discover, in a short crack with a neighbour that some foul fiend had chained it.
       What I fail to understand is WHY? Unless it's hair-splitting?  So far as I'm aware a lack of yellow lines means parking is possible/permissible, particularly on a straight road, in a Housing Estate?  The thing is - as far as I can see his/her back wheel is forrard of the lines - BUT - if you dropped a perpendicular from its rear end you'd, probably find a tiny portion of it might be above the lines.  What I wonder, is/are the criterion/criteria?