English language requirement - Masters / Bachelor degree

Hello,

I am currently on a Tier 1 visa and hoping to move onto an unmarried partner visa. I see the application form wants me to prove (all over again) that I can speak English.

For the Tier 1 visa I used my masters degree from Cambridge to satisfy the requirement. With the unmarried partner visa they have a note that they only consider bachelor degrees. Mine was taught in South Africa so I would need to pay to establish it was in English. I am thinking of just using my Cambridge degree certificate regardless as evidence that I can speak English.

Any advice? Can they refuse my application on this basis?