Apparently the torture depicted is historically accurate. Here's more info from Wikipedia:
The most famous case in the United Kingdom was that of Roman Catholic martyr St Margaret Clitherow, who (in order to avoid a trial in which her own children would be obliged to give evidence) was pressed to death on March 25, 1586, after refusing to plead to the charge of having harboured Catholic (then outlawed) priests in her house. She died within fifteen minutes under a weight of at least 700 pounds (320 kg). Several hardened criminals, including William Spigott (1721) and Edward Burnworth, lasted a half hour under 400 pounds (180 kg) before pleading to the indictment. Others, such as Major Strangways (1658) and John Weekes (1731), refused to plead, even under 400 pounds.