Drafty UPVC front door

[wobbly2]

There is draft and external noises coming through my uPVC front door.

• The draft and noise is only noticeable in the middle section between the door hinges.
• Pushing the middle of the door toward the frame on the hinge side stops the draft and noise.
• The door appears to be slightly bowed away from the from the frame on the hinge side (I checked it with a 1200mm metal rule).

There is plastic tang(?) fixed to the hinge side of the door in the the middle (see photo). This tang looks like it could be for pulling the middle of the door on the hinge side toward the frame when closed but there is nothing for the tang to act against.

Can someone advise if the tang on the side of the door is for pulling the hinge side of it into the frame and, if so, what should be on the frame for the tang to act against and also if it is something that can be bought separately?

Update:If the tang is not for pulling the door into the frame would replacing it with a middle hinge solve the problem? The existing hinges are the flag type.