In message , at
17:11:00 on Fri, 27 Aug 2004, Richard J.
remarked:
Vistor Travelcards are designed for overseas visitors, and cannot be
purchased after arrival in London. In the UK, they can be purchased
only as part of a London holiday package through certain travel agents.
They work out more expensive than one-day or weekly Travelcards unless
full use is made of the discounts to tourist attractions.

But as has been mentioned, they work all day. A tourist might want to
get out and about early, to make best use of the day, rather than
lounging in bed until 9.30!
--
Roland Perry