I must give credit to Linux Format for pointing me in the direction of this great little utility; nethogs allows you, as the name suggest, see what is consuming / hogging your network bandwidth.  Unlike iftop, which shows you the source and destination ip/port.  nethogs simply shows you the processes that are running that consume bandwidth.

nethogs

To Install nethogs in Ubuntu.

sudo apt-get install nethogs

it has to run as root, and if eth0 is not your active network device, pass the device e.g. eth1 as the first parameter.

sudo nethogs eth1