[regularfry]

Yeah, the more usual wording is "given a free rein", which makes it a little clearer. A monarch isn't given their reign, it's theirs by right (well, with a bit of hand-waving. Or possibly sword-waving, but not since Henry VII).

[rjsw]

The last English king to try to reign with no constraints was Charles I, it didn't end well for him.

[Zuider]

James II entertained the same delusions as Charles of being absolute monarch. He had a kinder fate, being carefully allowed to escape twice on his journey to France.

[pasc1878]

For English kings you forgot William III

[dash2]

Actually I think the last king to go into battle at all was George II.