Nexus 5 from Canada in the UK with UK SIM?

[Origin]

Does anyone know of any issues with me doing this? I'm coming home for a couple of weeks and would like to put a UK PAYG sim in my old Nexus while I am there.

Is there any problem with this? Should I / Will I need to root / flash it for 4G?

Anything else I should be aware of?

Thanks