National firm Shoosmiths is preparing to put the Mayor of London Ken Livingstone on the stand as it acts for Thames Water in a forthcoming planning inquiry.
Head of planning Iain Gilbey has spent the past five years working for Thames Water, advising on a proposed £200m desalination plant in Beckton, East London.
In April, Livingstone rejected the proposals, saying that putting energy into extracting water from the River Thames was a waste when leaks in pipes could be mended instead.
A public inquiry kicks off on 23 May and is expected to last for five weeks. Gilbey has worked closely with Thames Water's in-house team, led by Simon Byrne, throughout the five years that the plant has been in the planning stages.
Livingstone will be a witness in the inquiry along with senior Thames Water personnel.
"Thames Water's proposals for a desalination plant are an important part of overall strategy for water delivery for London and the South East," said Gilbey.
He added that instructions from the company over the Beckton plant came shortly after he moved to Shoosmiths from Ashurst in 2000.
Byrne said that, because Shoosmiths was involved on preliminary issues, the firm was a natural choice for the inquiry work. "The inquiry is being conducted on a team basis," he added.
Gilbey has instructed 2 Harcourt Buildings' Keith Lindblom QC for the inquiry.