Southern Water's shareholders will bear the entire cost of this fine.

Ofwat chief executive Regina Finn said: "Southern Water behaved unacceptably in deliberately misreporting customer service performance to Ofwat and systematically manipulating information to conceal its true performance over an extended period of time and the company has acknowledged this."

The obligations on the companies to provide accurate and reliable data are designed to protect consumers in a monopoly environment. Without a choice of supplier, this protection is essential.

"We expect companies to comply with their obligations and this fine sends a clear message that non-compliance is not a cheap or easy option," said Ms Finn.

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