In my quest to find the a solution to my issue I Googled "Morgan Plus 4 Starting Issues" and it took me to a post on this website where back in 2018 DaveW gave some ideas/solutions re the problem, so off out to the garage I went rubbed the black plastic end part of the key across the key hole barrel by the immobliser sensor "ring" and hey presto the dash immobliser light went out, popped the key in the barrel, turned it and she fired up first time. Tried it several times and any time it didn't start a quick rub got the immobliser light out and away she went.
Now to find a permanent fix. Many thanks Google, Talk Morgan and in particular DaveW.
Cheers Dougal