What exactly were THE LAST VICEROY's views, other than not wanting to be a military dictator?
Mildly left of centre in a very paternalistic and somewhat authoritarian kind of way, interested in technocratic solutions to difficult problems, pro-environment before that was fashionable.* Had he not been murdered there's little doubt that he would have looked favourably on the SDP.
*Quite a similar package, overall, to those of that other mid-century Modernist titan Lord Reith, which is amusing as Mountbatten was on Reith's constantly updated Enemies List.