According to
this analysis (adobe acrobat reader required), which mostly relates to the idea of using churches as sanctuaries for illegal immigrants from countries with bad civil rights records and such, but starts out with some history of the church as sanctuary. Apparently it's a matter of church rather than civil law, and has been banned in England since the 1620s and in France since the French Revolution. So, basically, it's illegal at this point. The concept no longer exists.
I also suspect that if the individual claiming sanctuary while it WAS possible was in fact guilty of some major crime, the priest would spend the time trying to convince the miscreant to place his life in God's hands or whatever, and give himself up to the authorities. The same kind of thing that they are supposed to do today if someone confesses a crime.
There may also be question in terms of what churches would have the right of sanctuary to begin with ... The Roman Catholic Church, certainly ... I'm not so sure about the protestant denominations.