Mike has your brother initiated proceedings to take the situation to the tribunal to have the tenant forcibly removed? The other option is to initiate small claims court proceedings (though he will have to be very quick as it is rapidly becoming more than a small claim) - if he does this it might be enough to get the tenant to piss off if he wants to avoid the debt, or alternatively if he stays and it goes to court your brother should at least get his money back over time.
