How to transform objects along last-used axis using middle mouse and drag?

TL:DR - When I try to transform an object using the middle mouse button the camera pans instead.

Hi total noob here!

It says in the Unity manual that you can click and drag the middle mouse button when using the move, rotate and scale tools to adjust the last used axis - i.e. the one that is currently yellow. Being a Maya user I've come to love this functionality, but whenever I try to use it the axis handle turns back to it's regular colour and the screen pans instead - something I would associate with the alt-middle mouse camera panning control.

Any advice would be greatly appreciated :)