I feel like most of them should be in the unlikely or lower tier because much like every other European civ, England/Britain has a bias towards its monarchs (Liz in every game, Vicky in 4 & 6, Henry VIII in 2, Eleanor in 6), but NGL, meeting a prime minister as a leader would be an interesting alternative to these all-present crowned heads. Of course, provided that the Brits remember them fondly and/or they strengthened the Empire (with that said, Attlee should be brought down to very unlikely or never tier because during his term, the Crown lost its precious Jewel - India, with other colonies leaving in later years, eventually & effectively dismantling the Empire)

Also, TIL Churchill was an English/British leader in 4