Have been using USB midi controller however MuLab doesn't seem to respond to my usb midi interface even though the interface shows in the midi preferences!

What I'm wanting is to use and external midi interface to run midi to external gear.. Does someone have an answer?

Hmm - There is a rare problem on OSX where you need to double check your MIDI device to make it run, and another ultra rare problem where you then need to press 'panic' to make it work.

No idea what it could be if you're on windows...

I am on windows...

Session menu -> Show Session Modular Area.
There you should find a MIDI Output module. If not, create one.
Drag-drop this module on a track, so that the track plays this MIDI out module.
Now the events on this track will be sent to MIDI out.

If you want to use multiple MIDI ports, create a Patch Point for each MIDI port you want to use and connect it to the respective MIDI ports. Then connect tracks to these Patch Point.

Does this help?

Yes and one Midi output module(=midi port) stands for 16 midi channels ?

Yes.