Ashamed to admit this, but I made a school boy error!
Checked & re-checked the leads today & then it finally dawned on me to check the firing order.
Checked which leads were going to which spark plugs. Leads 1 & 2 were the wrong way round.
Swapped the leads over at the spark plug end & fired it up. Bingo - no misfire at all.
I must have done it when I renewed the spark plugs!
Thanks everybody for all the tips & advice.
Runs like a dream now. Got the correct coil too!
Edited by Readers14, 25 June 2017 - 08:17 PM.