Westminster and Middlesex Commission of Sewers
The Westminster and Middlesex Commission of Sewers was established in 1596 under the 1531 Statute of Sewers. Its area was defined by statute in 1807, and before then by various letters patent. It was absorbed by the Metropolitan Commission of Sewers (which took over the Greek Street offices) on 1 January 1849. Records are kept at the London Metropolitan Archives

References

History of local government in London (pre-1855)
Water supply and sanitation in London
Former water company predecessors of Thames Water