You can apply to court to extend the 21 day period for registration if you can satisfy the court that the failure to register in time: was accidental, due to inadvertence or to some other sufficient cause; or was not of a nature to prejudice the position of creditors or shareholders of the company; or should otherwise be allowed on just and equitable grounds. If a court allows an extension of time it is likely that any charges registered in the intervening period will have priority over your ‘late’ charge.