This is a case that Euan Roger has tweeted about, with a toilet humour twist, but also some interesting early uses of mitigation claims in court (i.e. defendants’ appeal to loopholes to escape capital punishment).
On 4 February 1402 a coroner was summoned to the church of St. Mary Somerset in London to hear the confession of sanctuary seeker John Giffard of Devon. Giffard confessed that he had, with five other men, broken into John Staverton’s house at Ipswich and stolen 80 marks (about £54) in goods and money. The coroner’s memo, however, did not then follow with the usual indication that the confessed felon abjured the realm, probably because of what followed.
Soon after this confession, Giffard was in court at King’s Bench charged with the felony of burglary (my thanks to Euan Roger for alerting me to this part of the case). Rather than pleading either guilty or not guilty to the burglary, Giffard pleaded sanctuary: that is, he claimed that he had been illegally dragged out of the church and taken into custody. He asked the court to restore him to the church. The question of whether he had, in fact, been illegitimately seized from sanctuary was put to a jury: if the jurors found his claim to be true, he was by English law to be returned to the sanctuary to proceed to abjuration.
The jurors, however, ruled that when he was arrested he was outside the sanctuary, having left there of his own free will. They reported that he had gone to a “communem latrinam,” a public toilet, one hundred paces away from the church, and arrested on his way back.

The jurors questioned whether or not he could have emptied his bowels somewhere closer, and they answered that he could have done so just outside the churchyard. (This raises interesting logistical questions about the usual toilet arrangements for sanctuary seekers…). Euan Roger did some work to figure out where this public latrine might have been – and decided that it was likely the facility at Queenhithe, about 100 yards away from St Mary Somerset churchyard.
So Giffard was denied his sanctuary plea, and as he had already confessed his felony he was to proceed to execution. He was, however, able to pull another mitigation out of his pocket: he claimed benefit of clergy. Giffard’s claim to be a “clerk” (cleric) was tested by giving him a bible to read; he “read it like a clerk,” and so was handed over to the church authorities for punishment (around 1400, this likely meant that he was released after a relatively short time, having done penance). This didn’t mean Giffard was actually a priest; although benefit of clergy had originally developed so that the church maintained its jurisdiction over its own personnel, Giffard is probably a fairly early example of a layman being able to claim clerical status as a way to avoid the noose.
Around 1400 benefit of clergy was becoming a legal fiction by which any man who was eligible to be a priest – that is who was literate and had been married only once – could claim, for the purposes of a felony trial, to be a member of the clergy. A successful clergy claimant was transferred to the ecclesiastical authorities for punishment following conviction for felony. The church did not execute offenders, and thus this saved the felon from capital punishment.
As women were not eligible to be priests, they could not claim benefit of clergy whether or not they were literate; it was a male-only privilege. Moreover, as the main test was based on literacy, and literacy was highly dependent on social status, it was also biased by class. The number of benefit of clergy claimants also became much larger by the late 15th century, partly because of increasing literacy, and partly because the judicial system in general was friendly to the use of mechanisms that allowed the elite to escape execution.
Actual clergy (more commonly charged with felony than you might think – here are a few who sought sanctuary) could of course also claim it.
TNA, KB 9/187, mm. 36-37; KB 9/189, mm. 46-47 [another indictment involving Giffard, where the burglary victim in the case he confessed above, John Staverton, was one of the JPs hearing the case]; KB 27/563, rex m. 19; Sayles, Select Cases in KB, vol. 7, SS 88, 120-21. Image at top: Maestro di Jean Mansel (1430-1450), illustration from Boccaccio’s Decameron, http://www.enteboccaccio.it/s/casa-boccaccio/item/1319