Green Euro MP Caroline Lucas is to ask the water watchdog to end Southern Water's right to supply thousands of customers in Sussex and the South.
She said she was taking the action because of the way the water company had dealt with its planning application to build a huge sewage treatment and sludge recycling centre at Telscombe Cliffs.
Dr Lucas, who was elected last year as the South East's first Green Euro MP, was giving evidence to the Portobello inquiry into Southern Water's proposal to upgrade the existing sewage treatment works
She was warmly applauded as she outlined her threat to end Southern Water's licence to operate.
Dr Lucas said there had been "a serious breakdown" in the management within Southern Water over the way they had dealt with the issue of trying to find a suitable site for a new treatment works to serve the Brighton area.
She said Southern Water knew that such a plant could not be commissioned within three years and they would be unable to meet the deadline required by the European Union to provide cleaner bathing water off the Sussex coast.
She said this showed Southern Water was "naive" in its thinking.
Dr Lucas added: "I must put the management and shareholders of Southern Water on notice that I will be writing the the water regulator inviting him to consider revoking Southern Water's licence to operate."
OFWAT, the water watchdog is responsible for licensing water companies and keeps an eye on their charges to the public.
Dr Lucas, a leading member of the Green Party nationally, said she believed Southern Water's appeal against East Sussex County Council's refusal to allow it to expand its existing Portobello works was "fundamentally flawed".
At the inquiry Southern Water is appealing against East Sussex County Council's decision to refuse planning permission for the expanded works.
Last night Southern Water said of Dr Lucas' threat to try and gets its licence revoked: "This is entirely a matter for the water regulator".
The spokesman added: "All matters regarding the Portobello planning application are currently being fully aired at the public inquiry so the right decision can be reached."
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