You do if you are doing on a building site for a reputable building company they will-should ask for a copy of it,I have to send in copies of up to date insurance every year before another contract is issued.
You dont need ANY insurance to clean windows period
If you are cleaning windows on certain properties you need insurance I’ve just sent 3 copies off for yearly contracts,ok you say you don’t need it for “Cleaning Windows” I can assure you you’re wrong Housing Associations all ask for it. If you just go out cleaning windows and the pole drops on a 150 grand car good luck with that one.