Hi kentishman.
It's a good job he is an Optician then. Metformin and Avandia (Rosiglitazone) are commonly prescribed together. There is a combination version called Avandemet as well.
I was on the self same meds for quite some time before being changed to Pioglitazone and Metformin instead after being given Byetta. (Rosiglitazone is contra indicated with Byetta).
The Pioglitazone was also stopped shortly after.
So all in all....your GP seems to know what he is doing.
Ken.