Hi Jo, and thanks for your help.
The floor of the shower is faulty and needs to be ripped up and repaired. The shower will definitely be unusable, and given the mess, debris, and storage of equipment I assume the bathroom in general will be difficult to use as well. I am in London in case this matters.
No. There is one large shower with tile flooring and that is all.
When you say entitled to a deduction in rent, is that a legal responsibility of the landlord?