Ok... further information...
As suggested in another forum I forwarded ports 7240 and 7241 UDP...
I used PFPortChecker and confirmed the ports were forwarded and working.
I then used Process Explorer, followed by AW Ports Traffic Analyser to check if the ports were in fact correct.
Sure enough the mb_warband.exe has UDP ports 7240 and 7241 open.
The 7240 appears to be the server list reporter as it sends a message with the server settings (and some other binary stuff) to an IP address (41.232.45.4

periodically and I can only assume that port 7241 is the main game port...
My friend could not see my game in the list...
MAIN QUESTION: Can we connect directly to an IP address, thus bypassing the whole server browser?