Evening Clive,Only just got to looking in detail at your supplementary questions, but you have found the website that I was using to make my assertions.
You are right, the top four lamps look like the signal aspect indications (though quite how they worked for the multi headed beast I'm not sure) and below that the three indicators for the route set. Note that the 'route' is illuminated even though the signal is red (inside, not to the driver) so that the signalman knows he has pulled the right points before clearing the signal. From the signalling plan, there are DF and DS for North and South lines: the indicators show DF DS and (annoyingly) 'D?'. I would love to know what the third indication was to know whether they were fitted left to right or right to left.
Paul.