A quick update, turns out to be the ignition switch so I've ordered a new switch and tumbler - it's a two part assembly. Cost around 140GBP.
BTW - I first looked at the ignition immobiliser and bearing in mind it was fitted by 'qualified and authorised' insurance alarm fitters found two chassis ring terminal connections where the fitters didn't bother scraping the paint first
So I'm surprised it actually worked in the first place!
Turns out this wasn't the cause though and was definitely due to the switch. If I carefully turned the switch to ignition then backed it off fractionally I could reproduce the flashing IC panel. I also noted that the positions were not as defined they should feel so hence the reason for purchasing both barrel and switch.
Now simply waiting for the matched barrel to arrive from Germany
For the reference of others here's the removal video:
http://www.mbca.org/northtexas/repair_videos.htm
Lea