As I've often said if you aren't upsetting the socialists and the anti British then you ain't doing your job. Popular PMs just don't do any major changes. Any change wll upset some group or other. Can't make an omlette without breaking eggs. With MrsT the medicine was harsh but didn't the patient need it.
If we're basing popularity or otherwise on how long the PM serves then Alec Douglas-Home presumably jumps to the top of the list. But then not that far behind him was Anthony Eden and I think he was about as popular as PMs get, at least with the people.
Tony, I've always lived south of Watford Gap - and I utterly detested her - but then the red mist of an unworkable and out-dated Labour philosophy was clouding my judgement. That said, my personal opinion of her at that time doesn't make her the most unpopular Prime Minister.
(What is it with some northerners banging on constantly about a north/south divide? It's a prejudice that I really don't understand that at all).