I've never heard anyone say it aloud and it's driving me nuts.

It's a Greek name, so I'm thinking "issi-GO-nis."

But, since he spent most of his time in the UK he may have said "Is-SI-gonis."

Can anyone give me a definite answer?

 

A number of YouTube videos cover the history of the Mini and they pronounce his name. The videos are outstanding. Search on "history of the Mini".

 

I've only heard it pronounced "issi-GO-nis."

 

If you want to add a flair of bonhomie or panache, simply refer to him as Sir Alec.