Unless a contrary intention appears expressly or by necessary implication, there shall be implied the covenants relating to the right to mortgage, quiet enjoyment, freedom from encumbrances, further assurance, maintenance, repairs and protection of the mortgage security in the terms set out in Part I of the First Schedule; and where the mortgaged property includes a leasehold as to that leasehold there shall be implied the further covenants relating to validity and past and future observance of the lease in the terms set out in Part II of the First Schedule.