On Mon, 20 Apr 2009 17:35:20 +0100, Barry Salter wrote:

The key anomaly is that Vauxhall is a London Terminal but is NOT a
London Group Routeing Point. It has London as a routeing point but
also has Clapham Junction. According to map OV, which controls both
flows, the only valid route from Watford Junction to London Group
Routeing Point is directly into Euston -- but from Watford to Clapham
Junction (and hence Vauxhall) map OV takes you down the West London
Line.

However, given that the single fare to Clapham Junction is higher than
that to London, you're not actually allowed to use Clapham Junction as
a Routeing Point. London would be the only Routeing Point for
Vauxhall.

However, Watford Junction is a routeing point, and London is a (Group)
routeing point, so you don't have to do a fares check to determine valid
routes, just check the map(s).

As stated above, Vauxhall isn't part of the London Group routeing
point. So you do have to do the fares check.