Citizens Advice probably won't entertain it too much as you've all signed the contract to live there.
I think also it's just out of natural hygiene that you all take collective responsibility to ensure the cleanliness and condition of the bathroom whether you all rent as a group or individually.
If you're talking about maintenance and disrepair of the bathroom (mould, damp, large cracks in walls/ceilings, leaks) then yeah that's down to the landlord to replace. If it's come in to disrepair because no-one can be arsed to clean it it's not always going to be the landlord's fault.