Cameron McKenna is acting on what is expected to be the biggest flotation this year - National Grid's sell-off of a minority stake in its telecoms arm, Energis.
Corporate partner Sean Watson is leading the 26-strong team advising Energis, the same team which, when part of McKenna & Co, advised National Grid on its own flotation in 1995.
However steps have been taken to deal with potential conflicts of interest.
Potential Energis shareholders will require a good value for their shares, while National Grid will want the best return possible from what amounts to a sell-off of its assets.
Watson said that, unlike the Zeneca demerger from ICI in which Linklaters & Paines acted for both companies, Cameron McKenna has become the lawyer for Energis in this transaction.
National Grid, he said, would instruct another firm or use its own in-house team in situations where conflicts might arise. He said conflicts had already arisen on some decisions in the four months that Cameron McKenna had been advising Energis on its options, but added that "a lot of people spent a lot of time ensuring that any conflicts that arise are properly managed".
Although Energis is not yet revealing what proportion of its shares it is selling, analysts predict the flotation will raise between £200m and £300m, giving Energis a total market capitalisation of around £1bn.
Dresdner Kleinwort Benson, the financial adviser, sponsor and global co-ordinator of the float, is being advised by Slaughter and May.