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.
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