Why did the British name an important tank after Cromwell when he has such a bad reputation in Britain? Wouldn't that be like the US naming a tank the Benedict Arnold?

British "cruiser" tanks were given names starting with a "C": A13 Mk II Covenanter, A15 Crusader, A22 Churchill, A24 Cavalier, A27M Cromwell, A27L Centaur, A30 Challenger, A34 Comet, and A41 Centurion.

The Covenanter was the earliest given a name; previous cruisers were called "Cruiser Mark III" or by their General Staff designation (like "A20"). With the profusion of tank designs in use at the time, this was rather confusing, or so thought Winston Churchill. He directed that names be given to tanks on 27 June 1941.

The names of the existing tanks are then to be attributed to David Margesson or General Sir John Dill (or someone on their staff), potentially based on informal names already in use. I do not have the response, unfortunately. Later tanks, like the Cromwell, would be named by their designers or the Tank Board, but the reasoning often doesn't make the historical record. For the most part they seem to pick names that are martial or impressive, but with no particular scheme. The Cromwell, however, continues a minor pattern (with Covenanter and Cavalier) of Civil War factions.

While I'll leave the historiography of Cromwell or the history of his perception in the UK to someone else, it seems that from the pattern of tank naming already established that Cromwell was a plausible choice and may have even been suggested by previous names. Further, it seems that at the time the name of a tank was not a public relations exercise, but mostly a convenience for those in government who had to talk about tanks a lot, so the reaction of the public was not much considered.