Thames Water deliver 2,822 million litres of water daily. They have a leakage rate of 895 million litres per day.
Source .
I am not sure if the leakage is factored into the total delivery (which would give a leakage rate of 31.7%), or if it is a separate figure (this yields a leakage rate of 24.1%). Either way it's absolutely terrible and a complete insult to those on hosepipe bans.