Flickering lights

[dustyv]

Hi,
My 1988 745 Turbo Diesel Estate has just developed an issue with the lights flickering.
Scenario:
Start the beast, after a short while, noticeably at idle, but occasionally does it under power.
Sometimes doesn't do it at all - but events of it happening are now becoming more frequent.
This is all lights, head, side, dashboard.
What could cause this?
The battery is new, the alternator was new (refurbished) about 5 years ago.
All connections have been checked (by me) and seem to be OK.
Could this be an earthing issue?
Alternator on it's way out?
Or something more sinister?
Obliged for all and any advice offered.
Thanks.