Not currently; if the system is overwhelmed and the treatment plants start backing up then untreated water will be released in an emergency to prevent sewer fro

Not currently; if the system is overwhelmed and the treatment plants start backing up then untreated water will be released in an emergency to prevent sewer from flooding up into the streets. They are currently spending 4.3B pounds to fix it with basically a giant holding tunnel: https://en.wikipedia.org/wiki/Thames_Tideway_Tunnel https://en.wikipedia.org/wiki/Thames_Tideway_Tunnel