i had sent them my original hsmp approval letter, FLR letter and the original ref letter from my University's Head of department. This letter contained both confirmation about my degree, year, and english language. This was dated from when i had originally applied for HSMP as i sent this then along with University Certificate, but i didnt want to send the certificate again.
Also if you have IELTS, i would send that, but make sure it is no older than 2 years as last time for my HSMP i sent one which was given at Student visa time and they rejected it. Later in appeal they accepted the proofs were sufficient as i had included UG University Certificate in computer science from UK.
Hope this helps!