Unable to host 64 bit

I am currently running Ubuntu 16.04 64 bit
I have installed Virtual box Version 5.2.12 r122591 (Qt5.6.1) 64 bit.
I have changed my bios to support virtualization.
The only option I have is to host 32 bit Guest OSs

Is there another setting I am unaware of that I also need to change?

Thanks