Thanks for your response. Sorry I didn’t get back to you on this… I was hoping you would be able to tell me whether my particular external hard drive was bootable. In the end, I found out the hard way that it isn’t! 
Luckily, we still managed to find an alternative solution to what we were trying to achieve.
I am still wondering though… is it because my external drive is old that it isn’t bootable? If I bought a new one, would that be bootable? I have read such conflicting things about this on the internet…
Cheers,
Chris (channeal)
