OK I did the obvious thing this morning and rang Brother.
For anyone who may in the future be interested: the advice from Brother is that the printer DOES transmit its own ad-hoc network (called SETUP) to which you can connect and print without the use of a router.
The advice also included that when connected to the printer you can no longer use wireless to connect to a router and the internet. For that, you would need to simultaneously use an ethernet connection or mobile 3G USB dongle.