Thanks for the comments - here is the response I got on another Landie forum.
"Series One station wagons uses 12v 21/5 watt stop and tail bulbs in both front and rear lamps. In normal conditions the flasher system flashes the 21 watt filament in the front / rear bulb on the side selected. The flasher switch is a special one that has both the flasher circuit connected and the brake lights. With the flasher switch in the off position the brake lights are connected together and work as normal when you operate the brake.
When the flasher switch is operated , say to LH Flash position, the LH brake light is disconnected from the brake circuit and used as the flasher instead. The RH brake light works as normal. The side lights ( parking) operate as normal. LUCAS made a relay DB10 which will do all this a well but Land Rover used the LUCAS PRS7 switch instead. Rover Part 2643702. Hella also do a similar switch which will carry out the same function."
So it would seem that it is the brake light filament that flashes.
This is the switch panel - it has the switch for the indicators and the switch for the interior light.

Thanks
Garry
REMLR 243
2007 Range Rover Sport TDV6
1977 FC 101
1976 Jaguar XJ12C
1973 Haflinger AP700
1971 Jaguar V12 E-Type Series 3 Roadster
1957 Series 1 88"
1957 Series 1 88" Station Wagon
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