A lender advances money to a borrower for twelve months with interest on the sum at 1 per cent per month. The borrower fails to repay the loan in full. The lender seeks the return of the outstanding sum, in addition to agreed default interest of 4 per cent per month from the date of breach. Is the default interest of 4 per cent unenforceable as a penalty? More specifically, how does the rule against penalties apply in circumstances where the default interest rate is also payable upon a number of events of varying gravity