[Ant]

Spoke to a mate at work, apparently it's due to your motherboard supporting legacy.

To fix this error, firstly you need to enter BIOS Setup to see what the boot mode it is set to. Start/restart computer and continuously press a key to enter BIOS before Windows logo appears. Different computers may require different keys, so you had better search "how to enter BIOS plus computer trademark or motherboard name" on the internet to find the exact key. 

In BIOS, if you find no signal showing you are using UEFI motherboard like the following picture shows, maybe you are using a traditional motherboard which supports legacy BIOS boot only. Under this situation, the only solution is to convert GPT disk to MBR disk.

He stated that the link : https://www.partitionwizard.com/partitio...-disk.html should help.
(this is where above info is from)

My motherboard can support legacy boots, UEFI Boots and USB / CD Booting. So I doubt that's the issue, but thanks for you're help

In the bios, what boot setting is selected?

Legacy Boot - Enabled 
Secure Boot - Enabled 
UEFI Devices - Enabled