Berwin Leighton Paisner (BLP) has landed one of its biggest transactions to date, after being instructed to advise the directors of Thames Water on the company's disposal by German parent RWE – expected to be worth up to £8bn.

The firm, which has worked with Thames Water in the past and is currently advising it on some procurement issues, won the instruction two weeks ago.

BLP corporate partners Patrick Somers (formerly at energy giant Lattice Group), Andrew Sherratt and John Hurdley, who heads the firm's water sector team in the utilities group, will advise Thames Water's directors, joining Slaughter and May and Linklaters on the deal line-up.

Graham Johnson, company secretary at RWE Thames Water, told Legal Week: "The directors of Thames Water asked the in-house lawyers to engage an independent legal adviser and we identified BLP. We
have worked with the firm on a number of commercial transactions. Now they will advise the directors in relation to the sale in case of any conflicts of interest."

Somers said: "This is a very significant deal for us. It underlines our expertise in infrastructure and water in particular. We are very pleased to be involved because as a firm we have been focusing on the area for some time and it also builds on and consolidates our existing relationship with Thames Water."

Slaughter and May is advising RWE with corporate finance partners Charles Randell and William Underhill leading. Linklaters, RWE's regular lead corporate counsel, is instead advising Goldman Sachs, which is overseeing the disposal.

Australian bank Macquarie and private equity house Terra Firma have both been cited as potential bidders.

Slaughters and BLP will work with RWE Thames Water's in-house legal services manager, Simon Byrne.