What does your NHS GP write on your fitnote?

Hi everyone,
This quesiton is mainly for those based in the UK but happy to hear the experiences of others as well.

I've been off sick for a while and my GP writes my conditions, but doesn't write anything in the "funtional affects" section. I am trying really hard to explain to work what I need in order to make a recovery, but they are limited by the fact they don't want to just ake my word for it.
I asked the GP to write a seperate letter for work explaining what I need and they refused, saying it's company policy not to write a seperate letter.

Just want to know if anyone else's GP writes anything helpful / specific on the fitnote?

Thanks