It looks like it’s a Grohe. Grohe do parts, also for their older models, but there is a cut off point I think.

Is it the rubber seal? If it is I used to remove mine by sliding it off from left to right. You can get replacement seals quite easily from plumbers merchants, DIY stores (if they are open) or online.

Hello, thanks for your replies. We don't have a deflector and was wondering if that would be the solution? However, the shower room is in the attic and the deflector may not be able to fit onto the glass screen without re -doing the screen that's there atm.... The actual shower is on the wall opposite the screen, and more water seems to run off that wall (which has wavy tiles), onto the grouting and off onto the floor. We're really happy with the overall result of the shower room...just need a solution to this niggly problem! Would be grateful for any other suggestions. Thanks

Unless you are very good at DIY I think I would call a plumber for this one. It looks like a bodge job and he might have to fix it properly. He may have used silicone to avoid piercing the damp proof membrane/course/coating behind. I would be wary of drilling into tiles too unless you have lots of experience.