Calling Londoners: has anyone else had trouble with a water bill following replacement of watermains?

[frogs]

In the autumn we had a bad case of the syndrome that seems to be all over North London atm, with huge diggers taking up the road to replace the Victorian water mains with shiny plastic pipes.

And now we've had our six-monthly water bill, for a grand total of over £900 (usual bill for 6 months is around £120). I've done a leak test, as suggested by Thames Water, and we don't have a leak anywhere in the house. Surely the water mains work must be related to our insane bill? That is such a vast increase in usage that it goes way beyond anything we might have done ourselves, such as one of the children leaving a tap on overnight.

Anyone else had this, before I go to do battle with Thames Water?

No experience of this, but definitely call them and tell them it is not possible that your bill is so high and that they have made a mistake. Get them to justify what they are charging. If they stonewall, keep asking for people's bosses and make sure you get their names (it puts the wind up them).
I once called London Electricity on something like this and asked them to justify their charges (c. £90 when I wasn't living in a flat). They eventually admitted that they had no idea how they calculated it and said "will you pay £16 instead." I said I would think about it and no bill ever arrived...

Good luck!