Nah don't worry, I just spotted it before you did. Does all look like someone was in hurry though. I wonder if the bit of yellow in the background is the bonding cable, or that they forgot to stick it on.
Thanks for all the advice - it's definitely the strainer needing a good clean. Couldn't pull the cartridge out but all the prodding and twisting has helped - just put it all back together and the flow is greatly improved.
I will give RWC a call on Monday to see how the cartridge can be released.