I’ve just found this.
'St Sepulchre had a large population, and a high death rate, so like most city churches had difficulties with finding burial places. The space immediately around many churches, including St Sep. was crowded in with development, and noticeably higher than the church where it was still open ground, due to the number of burials. The church authorities established a separate burial ground in Chick Lane, and the majority of burials from the mid-18th century took place there, thus 'Chick' or 'The Chick'. Some burials (generally though there is no totally consistent pattern) the better off were buried in the Bay, ground which was still available adjacent to the church. The really well-off (or church officials like parish clerks, beadles etc) might be buried in the church itself, thus occasional entries such as 'buried in the left ile' - ile is what is now spelled aisle.'