@Arthur Thanks for all your help with getting this resolved
I have finally got this to work and this is what I did...
I installed Sketchup manually on a clean machine. It entered its 30 day free trial like it had always done previously. I changed the date on the machine forward 31 days to see if it would make any changes to the license file that was already present and correct. After I changed the date Sketchup finished it's 30 day trial but didn't enter into the free Sketchup Make mode and just locked down Sketchup asking for a license.
So I decided to start a fresh from the beginning...
I went to the Sketchup website to re download the .exe to extract the msi. I noticed that you can now only download 'Sketchup 2016 Pro' unlike 2017 where you can download 'Sketchup Make 2017'. This got me thinking, maybe you can't download and run Sketchup Make 2016 any more?
So I used my best friend Google and found an old installer for version 16.1.1450, extracted the msi and ran the install command with the original mst and license file that Arthur uploaded and it installed successfully.
This may seem obvious to most people but I thought I would document it in case others have the same problem in the future.