You can get a duplicate from the MOT station which originally tested the car, (about a tenner)
Car will be on the database showing it is MOT'ed so no worries about getting pulled by old bill.
You dont need the certificate when you next MOT.
You would need it if you Tax at post office rather than online, and also a buyer would want it, if you were selling car.
so pay a tenner or just wait until your next MOT is due.