A double mutant B-domain deleted Factor VIII gene having mutations at Phe309Ser and Asp519Val, respectively, is disclosed for use in the field of haemophilia therapeutics. The disclosure a double mutant B-domain deleted Factor VIII protein having mutations at Phe309Ser and Asp519Val respectively, is also disclosed, as well as methods of producing the same. The B-domain deleted Factor VIII protein having mutations at Phe309Ser and Asp519Val shows enhanced activity and stability and therefore is used in the management of haemophilia.