I don't know too much about this, to be honest, other than what I learned from Quasimodo in the The Hunchback of Notre Dame. I'm certainly no expert on church law, etc.
I've tried to find something about sanctuary, but I haven't had much luck. I did find this, which was published by the Church in 1912.
The ecclesiastical right of sanctuary ceased in England at the Reformation, but was after that date allowed to certain non-ecclesiastical precincts, which afforded shelter chiefly to debtors. The houses of ambassadors were also sometimes quasi-sanctuaries. Whitefriars, London (also called Alsatia), was the last place of sanctuary used in England, but it was abolished by Act of Parliament in 1697. In other European countries the right of sanctuary ceased towards the end of the eighteenth century.If this is accurate, then those refugees in St. Patrick's or those in Belgian churches are claiming a right that no longer exists. (I'm not sure they have claimed sanctuary in a church - it seems to be mostly their non-Muslim supporters who are referring to sanctuary.)
