In article , Peter
Able writes
IIRC Ongar used to be the tube station most distant from central london and
that only closed in 94.
That was my first instinct, but from Clive's website I see that I was
wrong !

As already discussed, it depends on what you count as "Central London".

My instinct is to use the Circle Line as the point to measure to. On
that basis (all numbers rounded):

Brill: 81 km
Verney Jn: 80 km
Quainton Rd: 70 km
Aylesbury: 60 km
Chesham: 42 km
Amersham: 38 km
Ongar: 37 km
Windsor & Eton Central: 35 km
Epping: 27 km
Uxbridge via Acton: 27 km
Uxbridge: 26 km
Watford Jn: 26 km
Watford Market via Finchley: 26 km
Upminster: 24 km
Heathrow: 23 km
Bushey Heath via Finchley: 20 km
Ealing Broadway: 20 km
High Barnet: 16 km
Edgware via Finchley: 16 km
Edgware via Golders Green: 14 km
Morden: 14 km
Mill Hill East: 11 km

--
Clive D.W. Feather