''Posturing outside court is highly undesirable,' said Mr Justice Potts at the start of the second day of a judicial review hearing.
Greenpeace and Lancashire County Council want the judge to qash the Government's decision to authorise the operation of British Nuclear Fuels' new Thorp nuclear reprocessing plant at Sellafield, Cumbria.
Alvin Shuttleworth, the state-owned firm's legal director, appeared on BBC Television news programmes on Monday night. He is a key witness for British Nuclear Fuels during the week-long hearing.
'The gist of it (what Mr Shuttleworth said on camera) seemed to be that Greenpeace seemed to be acting unreasonably or irrationally in bringing these proceedings,' the judge told the firm's barrister, George Nelson QC, adding that his judgment would not be prejudiced by the television interview.
He objected to Mr Shuttleworth's comments because Greenpeace and Lancashire County Council had mounted a legal challenge and there was a case to answer. 'It is entirely undesirable for witnesses to give interviews outside this court during the course of a hearing such as this. Posturing outside the court is highly undesirable.'
Greenpeace and Lancashire County Council argue that there should be a public inquiry into the granting of authorisations which the company needs in order for the pounds 2.8bn Thorp plant to discharge radioactive emissions into the air and the Irish Sea.
John Gummer, Secretary of State for the Environment, and Gillian Shephard, Minister of Agriculture, granted the authorisations at the end of last year. There was a public inquiry in 1977 into whether Thorp should be built. Greenpeace says that in the years since, the economic, nuclear proliferation and public health and safety cases for Thorp have all changed fundamentally.