Date of 18th century English gentleman's portrait

[LilyS]

Hello, I'd very much appreciate a date estimate for this portrait of my 4x great-grand uncle who was born in 1759. He was a corn and coal merchant in the English county of Norfolk in the 1780s, and later took up farming.
His collar has confused me because it doesn't seem to fit contemporary fashion. Might he have been a Presbytarian?

 

[Jonathan]

Definitely English... it's about 1783. The collar is just a lighter colour in a contrasting white wool or velvet, nothing religious, just typical of English men's tailoring of the time.