Is Boris Johnson the worst post-1945 Tory Prime Minister
Winston Churchill 1951-1955. Presided over the rise of the Cold War with Russia
Anthony Eden 1955-1957 Involved Britain in the imperial debacle of Suez
Harold Macmillan 1957-1963 Remembered for the Profumo affair
Sir Alec Douglas Home 1963-64 No notable ‘achievements’
Edward Heath 1970-74 presided over industrial strife
Margaret Thatcher 1979-1990 Laid waste to UK industry
John Major 1990-1997 Privatised railways. Famous for liking peas
David Cameron 2010-2016 Pioneered modern Conservatism. Gave up
Theresa May 2016-2019 No notable ‘achievements’
Boris Johnson 2019-2020 presided over significant COVID-19 death toll
I don’t think you need any qualifications after ‘worst prime minister’ – he has no rivals for that title.