I have A 1984 V12 lucas AB14 AMPLIFIER.
Is there any chance that the amplifier could cause the rev counter to dance about when ideling?

 

By far the most likely cause Rex! But check all the connections to the coil and the actual bullet connector joining the amp tach wire to the loom. Also check and clean the connector poles in the V, sited between the dizzy base and the amp. Also, if you have not done so, disconnect the condenser wire inside the amp box and see if all that helps.
I am assuming that the tickover itself is smooth and even?

Remove item C to disable the condenser

 

Cheers Greg. Idle is smooth and today sometim
showing 2000 when ticking over at 800 I have a look at
Those points you've pointed me to