The guarantee referred to in regulation 10 shall be entered into only—
(a) where the loan is to be made for the purpose of purchasing a dwelling house, upon satisfactory proof of the purchase by the mortgagor of the dwelling house and on production of an approved mortgage executed by the mortgagor and the mortgagee securing the repayment of such loan;
(b) where the loan is to be made for the purpose of constructing a dwelling house, if the dwelling house is constructed in accordance with the plans and particulars as approved by the Authority and upon presentation of an approved mortgage on the said dwelling house executed by the mortgagor and the mortgagee securing the repayment of such loan.