Joe wrote:
http://www.tfl.gov.uk/tfl/fares-tick...be-group.shtml

Note that this is a *group* ticket, valid only for members of a group of
at least 10 adults and/or children travelling together at all times.

Is this off=peak only,

There are no time restrictions.

and Is it really 80p for Under 17s, that seems very cheap?

It's actually 80p for under-18s. All this information is in the fares
leaflet, for which a link is provided on the web page you referenced
(though they got the page number wrong, it's page 20 of the leaflet =
page 11 of the .pdf file).

--
Richard J.
(to e-mail me, swap uk and yon in address)