Pip,
This is common on Minors, especially with dynamo fitted.
The reason the ignition light flickers on idling is the dynamo is not actually charging the battery. When revs increase the ignition light extinguishes and charging recommences.
I have had a similar problem when stuck in a traffic jam. If the ignition light glows quite brightly does this mean the battery isn't charging or the dynamo isn't generating! I've heard that the voltage regulator acts as safety circuit breaker - if the battery is fully charged the votage regulator cuts of the supply of current from the dynamo to the battery and prevents both from being damaged! Thus confusing the ignition light 'thinggie' thinking it isn't charging! Is this true?
When the engine revs are low enough and the dynamo voltage output is less than the regulator adjustment is set, the regulator disconnects the dynamo from the battery to prevent it becoming a motor. I think! As long as the light goes out on increase of revs, should be o.k. Never fiddle with theregulator though you could be opening a can of worms.
If you are lucky enough to have a good engine,properly set up
it will be capable of idling quite slowly. When Minors and similar
cars were new it was the done thing to set the tick over so slow that
the red ignition light was glowing. As has been said above there
is nothing wrong at all if the lamp glimmers at tickover, as long
as it goes out when you increase the revs.
Willie