If its large patches especially near hedges then you need a few people to give you a hand mate. You need a few sets of ears eyes imo. I would say don't bite off more than you can chew mate or you will just end up losing your ferret mate. Some of those burrows in the brambles are quite likely to be connected to the burrows in the hedge. You could start cutting some tracks through the brambles so you can set some stop nets, if you don't the bugger will just running back and forth.
Just my opinion mate.
Maybe invest in a strimmer cut the brambles into smaller blocks you can handle mate