A curious entry in John Evelyn’s diary, and the only one I’ve found concerning sanctuary:
 25th March. Good Friday. Dr Tenison preached at St. Martin’s on 1 Peter ii. 24. During the service, a man came into near the middle of the church, with his sword drawn, with several others in that posture; in this jealous time it put the congregation into great confusion; but it appeared to be one who fled for sanctuary, being pursued by bailiffs. [vol 3, p.219]
This is strange for a number of reasons. Firstly, it’s the only mention I’ve yet discovered of refuge being claimed in St Martins in the Fields; it’s not listed amongst the ‘pretended privileged places’ in the Act of 1697, and there doesn’t appear to be a community of debtors inhabiting the environs. Secondly, it takes place in a working church; the post-reformation sanctuaries based on religious right were on the site of dissolved monasteries, as with Whitefriars and Montague Close. Does this mean that sanctuary was believed to be found in any church? Thirdly, the claim is made on Good Friday; I’m surprised bailiffs were working on a holy day. Evelyn, alas, says no more of the incident.
For the sake of clarity, note that this is St Martins In The Fields, on the north eastern corner of Trafalgar Square, the current church dating from 1726, and not St Martins le Grand, a very important sanctuary in the heart of the City before the reformation. More on the latter to follow, but in the meantime, read McSheffrey’s excellent article Sanctuary and the Legal Topography of Pre-Reformation London (nb: link fixed 5/8/2015).