In around 1270 Heston was made a separate parish under Richard, 1st Earl of Cornwall, the Lord of the Manor. Richard of Cornwall was King John's second son and had served in the Barons' Crusade of 1239, where he succeeded as a negotiator for the release of prisoners. As Saint Leonard is the patron saint of prisoners it is possible that Richard dedicated the church to the saint, although the exact date of the dedication is unknown.