Hi John
I have a copy on cd of the 1821 census for Chiddingly.
There was a John French but his age is slightly out. Unfortunately it does not give place of birth
cottage at Holmes Hill
John French, 63 head gardener
Catherine French, 62, wife
Henry French, 22, son
That makes a birth of 1758
I checked the Sussex Marriage Index and possible marriage for John and Catherine
at Mayfield on 11 July 1783 to Katherine Lavender
Also on the SFHG baptisms there was a John French baptised on 12 March 1758 to William and Grace French at Selmeston
Neither mayfield or Selmeston are that far from Chiddingly and those names might give some clues, although they might not tie in or be correct, do you have children's names?
Kerry