http://www.oystercard.com/use_1.php says that you can use an Oystercard on
"National Rail services in London ... You cannot use Oyster for travel on
mainline trains outside Zone 6 in London".

but

http://oystercard.com/buy_1_4.php#7 says "Pre Pay can only be used on the
following participating National Rail routes:" which does not include the
ones round here.

So if I understand right I cannot use my Oyster Prepay card to go from
Twickenham to Richmond on SWT and thence by underground. If I pay the
standard rail fare for this, then my Oystercard for the rest I will lose
out so I need to buy a one-day Travelcard from a shop, which defeats the
purpose of having an Oystercard. Or am I missing something?

--
Tony Bryer