Fable has it that the phrase alludes to the fact that on 17 Dec 1540 the abbey church of St Peter, Westminster, was advanced to the dignity of a cathedral by letters of patent...but ten years later was joined to the diocese of London, and many of its estates appropriated to the repairs of St Paul's Cathedral. But it was a common saying long before and was used by Wyclif about 1380: 'How should God approve that you rob Peter, and give this robbery to Paul in the name of Christ.
Creative accounting really !!