Passport query. My grandson who lives in China

recently applied for a new British passport as his had runout. His new passport has a different number to his old one, this has made his marriage certificate invalid. He applied for a Security Access form from the British passport office and after completing the form and submitting it he received confirmation letter from the relevant department confirming both passport numbers were his. He has had this letter translated by a company into Chinese and it has been stamped to say it is a valid translation. Does he need the Chinese embassy in Manchester to issue a stamp on these two documents to enable him to use in China?