Thanks the response. An Isable Blenkhorne married at Snaith in 1591, and there are a number of Blencarn / Blenkarn references in this area. In 1656 Thomas Moore married Mary Blenkarne at Escrick - both were from Terrington.
A Philip Blenkhorn / -harn appears in the Snaith registers as father at four female baptisms in the early 1760s (one died), and Ann wife of Phillip Blenkarn died at Snaith in 1810. The notebooks of 18th / 19th century father and son local historians from Terrington (both John Wright, held at the Borthwick) identify the latter as having moved to Snaith from Terrington, and I believe the 1760s references must be to him. It would not necessarily be that he changed his name, but that it became written that way by the parish clerk or whoever completed the regsiter entries. It was Blenkarn when he left Terrington!! Did you have any Phillips in the family in the early 19th century? It was a less common forename and may point to a connection.
From memory, a thorough review of IGI Blenkarns, -horns will identify others at Howden, and other locations not so far from Selby. I believe you should also therefore consider the possibility your origins may be as a Blenkarn, and from Terrington at that!
Let me know how you progress. I will check out any other non-IGI references I have in that area and revert.