Google "Gertrude Tardrew" - states she married John HEYDON (as opposed to HEDDON) 11.10.1765.
Worth a look.
Added:
The IGI have a Family Group Record:
John Heddon born c1740 Parkham, Devon
married 11.10.1765
Gertrude Tardrew born c 1744 Parkham, Devon
Their children:
1. Grace - christened 6.4.1766 Parkham, Devon. Died 10.2.1770.
2. Bridget - christened 12.1.1767 Parkham, Devon
3. Richard - christened 16.7.1769 Parkham, Devon
4. John - christened 29.3.1772 Parkham, Devon
5. Grace - christened 21.8.1774 Parkham, Devon
6. Bridget - christened 17.10.1777 Parkham, Devon
7. Samuel - christened 27.8.1780 Parkham, Devon
8. Thomas - christened 9.4.1786 Parkham, Devon.
Some listings have Gertrude marrying a John LEDDON (just to complicate things!)
Hope this info helps.