In ,
AndreaC typed:[i]
Bob Wood typed:
You wouldn't need to get it from/to a station, but from/to the
boundary

of Z4.

But in an earlier post the advice was:

John B Wrote:[i]
No, because a Travelcard is a season ticket and not (as you might
expect) a PTE ticket. And you can only buy tickets *from* BZn, not
*to* BZn...

And that has certainly been the way it has worked on SE Trains -
coming in to London from Headcorn I got a return to/from Elmstead
Woods, going out of London I got a return to Headcorn from/to BZn4...

Which takes me back to my original (not quite clear) question - which
station would I need a ticket for in order to get me into Z4 if coming
down from Milton Keynes?

If coming *from* Milton Keynes, you would need a ticket to the first
station in Z4.
If going *to* Milton Keynes, you would need a ticket from 'boundary Z4'.



--
Bob