Looking through the usual websites (for tourism in Cumbria, etc) I can't see anything on that would fill all the available accommodation.
Perhaps Barrow-in-Furness is just one of those towns that always has a shortage of accommodation? For example, around 10 years ago I was trying to help a lady who'd transport arrangements had fallen through and who thus found herself stuck in Ipswich for the night. She was prepared to spend up to £120 and thought that she'd have no problems but (because I knew how short of accommodation Ipswich was) I suspected otherwise. I phoned 53 hotels and B&Bs for her; 52 were full and the only vacancy offered was priced at £150 for the night. (I eventually put her onto the last train to Felixstowe, to stay in a pub near the docks).
So maybe Barrow is similar (i.e. everything gets booked up weeks in advance during normal times anyway)?