DICEGEORGE wrote:

A double lightswitch with a neon in it from one of the switches
would be good - is it legal to drill a neon into a lightswitch,

Probably easier to use a three position grid plate with two switches and
one neon indicator, not really sure if it'd be bright enough though,
they also do filament and fluorescent indicators.

It would probably be necessary to take a blue neutral to the switch for this wouldnt it?

Well it would save you from being naughty and using earth as the
not-live side of the neon.