Hi Sally
On familysearch.org (IGI)there is a record of a George DOWNCAN, b 10 Apr 1756, csd 23 May 1756, Woodhorn, father Wm Downcan. Quite a good match but of course might be wrong! You probably have George's marriage but just in case, Mary Sedgwick, 16 Jun 1783, Longbenton.
Good luck searching
Shirl