Camps - Why didn't Britain bomb the death camps?

Transcript
Extract from a letter to Prime Minister Winston Churchill by a Polish woman living in exile in Britain July 26th 1943

Catalogue ref: FO 371/34550

I am writing to beg you to stop German bestialities in Poland. May I take the liberty of suggesting the two measures by means of which this result could be achieved.

1) To send a force of Allied bombers to destroy the death camps at Treblinka and Majdanek. Those camps have been built and fitted specially for mass executions (gas and steam chambers in which several thousand people can be killed daily), it would take the Germans several months to rebuilt them, during which period many thousands human beings could be saved.

2) Immediate retaliation. I know this is a method equally strange to the British nation as to any decent minded people, but it is the sole and only one the Germans can and will understand. If they were told that a hundred of their villages will be razed to the ground by the Allied bombers, unless mass murders in Poland or in any other occupied country, are stopped, they would stop. And if they were made to pay with the blood of their own civilians for the crimes they have committed, they would not commit them again. We know that the culprits will be punished when the Allied Nations have won this war, but by that time they will have murdered thousands and thousands more of their victims whose lives could still be saved, if the Germans were made to pay for their crimes now.