How to remove this drain cover

[Mayim]

I was about to unblock this drain in my back garden but then realised that I couldn't remove the cover. The cover was installed by some builders as part of a large renovation project.

I have tried posting on various diy boards, but no one seems to know the answer. I was wonder whether any of you have something similar and could let me know how to remove it?

Can't you just stick your fingers in the grids and pull it up? You'd probably have to take the bottom of the drain pipe off first