An advertising watchdog has criticised British Nuclear Fuels (BNFL) for making "misleading" environmental claims.
BNFL - which runs the Sellafield nuclear reprocessing plant in Cumbria - boasted in a newspaper advert that its management of the site meant "the future of the environment is in safe hands".
But a member of the public contacted the Advertising Standards Authority (ASA) and complained that BNFL "could not predict what would happen to radioactive waste in thousands of years to come".
The ASA ruled the advert was misleading because BNFL "could not predict the effects of the Sellafield nuclear power station on the environment".
BNFL said they had no plans to use the advert again.
The advert appeared in a local newspaper and pictured a butterfly rising from a hand.
It began with the words: "The Sellafield team cares passionately about the safety of its workforce, the local community and the environment."
BNFL said the advert was designed to show waste reprocessing and clean-up work on the Sellafield site over the next 50 years would involve "no harm to the environment."
In February 1999, the watchdog upheld a complaint about an advert which claimed BNFL had "perfected ways to deal with all types of nuclear waste".