On 10 May 1790 Sir Benjamin Hammett brought a bill before the House of Commons "for altering the Sentence of burning Women", which was to finally abolish the punishment of being burnt at the stake for petty treason (killing of a husband) and high treason (almost invariably "coining" - making fake or adulterated coins). The Bill became law on 5 June.
(I might note at this point that this is not a post for those prone to nightmares.)
There's little around on the internet on the issue, beyond this draft article about the attitudes of the period that may have led to the abolition. (And an interesting case of Nimbyism, in that it suggests the moving of the site of execution from semi-rural Tyburn to heavily built-up Newgate may have played a part in the change.)
Sir Benjamin was remembered in Notes and Queries in the 19th century, but seems to have been otherwise little noted.
N&Q reports that he told parliament this was
"One of the savage remains of Norman policy, disgracing our statute book, as the practice did the common law."
The replacement punishment still meant being hung by the neck until dead, but when you read an account of the death of Eleanor Elsom in Lincoln in 1722, that does sound like a mercy. Like most women in the 18th century (except occasionally when practical arrangements went wrong, as in the famous case of Catherine Hayes in 1726, when the executioner was said to be drunk), she was, it seems, dead before the fire reached her, but what she had endured first ...
"She was clothed in a cloth 'made like a shift', saturated with tar, and her limbs were also smeared with the same inflammable substance, while a tarred bonnet had been placed on her head. She was brought out of the prison barefoot, and, being put on a hurdle, was drawn on a sledge to the place of execution near the gallows. Upon arrival, some time was passed in prayer, after which the executioner placed her in a tar barrel, a height of three feet against the stake. A rope ran through a pulley in the stake, and was placed around her neck, she herself fixing it with her hands. Three irons also held her body to the stake, and the rope being pulled tight, the tar barrel was taken aside and the fire lighted. The details in the 'Lincoln Date Book' state that she was probably quite dead before the fire reached her, as the executioner pulled upon the rope several times whilst the irons were being fixed." (From William Andrews, Bygone Punishments, 1899 quoted in "Sentence of Death By Burning For Women" in The Journal of Legal History, Vol 5, No 1, May 1984, pp. 44-59; p. 47).
As Sir Benjamin told Parliament, this was gender inequality, for men convicted of the same offenses were no longer subject to drawing and quartering and "women should not receive a more dreadful punishment than men". Plus "it had been proved by experience that the shocking punishment did not prevent the crime". (p. 55)