One downside of the ethercard library seems to be reliability or compatibility with some networks.
The new firmware has been performing perfectly at home and at work but at Build Brighton (the local hackspace) it hasn't. The DHCP lookup is taking several seconds which means I need to disable the watchdog timer otherwise it resets before its setup.

Once this completes it moves onto the DNS lookup, this was failing very regularly at Build Brighton so I am now overriding this with Googles DNS server which seems to have solved this problem.