In message m, Tim
writes
I have a zone 1-3 travelcard loaded on my Oyster card, and want to
travel from Clapham Junction to Kew Gardens. This involves getting a
train to Richmond then changing for Kew Gardens.

However Richmond is in zone 4, which I have always assumed means having
to buy an extension ticket (for something over a pound). This seems
like an unreasonable expense & hassle, since I don't want to go to zone
4 or to Richmond, it just happens to a necessary one-stop detour on the
way to Kew

Or Clapham Junction Willesden Junction, then change for Willesden
Junction Kew Gardens.

There again, you can transfer through Richmond without going through any
barriers, although staff sometimes spot-check passenger's tickets

Or Clapham Junction to Kew Bridge, with a 5-10 minute walk to the
Gardens.

--
Martin @ Strawberry Hill