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Pet owners should be banned from buying flea sprays at supermarkets because they contain chemicals which pollute the environment, a parliamentary committee said.

Baroness Shaista Sheehan wants the owners of Britain's 15 million dogs and 13 million cats to ask a vet if their pet needs treatment before buying a spray over the counter.

The sprays contain chemicals such as fipronil and imidacloprid which kill fleas but also harm fish because they end up in rivers and lakes when washed off pets.

Baroness Sheehan, who chairs the Environment and Climate Change Committee, said flea and tick treatments should only be handed out in rare circumstances.

Her report called Paws for Concern: Pets, Parasites and Pollution, finds owners are encouraged to routinely use sprays even when their pets are unlikely to have fleas.

She said: 'The overuse of household pet flea and tick treatments is the equivalent of using a sledgehammer to crack a nut.

'Pet owners deserve accurate, evidence-based guidance on the need for, and risks of, the existing and new chemicals which are being prescribed and the impact they are having on their pets, home and the environment.'

The Liberal Democrat peer has told the government to ban the general sale of flea and tick products from supermarket shelves and unchecked online retailers.

Baroness Shaista Sheehan says the sale of flea sprays over the counter needs to be banned

She used her report to raise her concerns about what she called a 'worryingly embedded' relationship between the pet pharmaceutical industry and the bodies responsible for regulating veterinary medicines and producing guidance.

The report estimates that 30 per cent of dogs and 20 per cent of cats received parasite treatments year-round, while an additional 50 per cent received some kind of treatment at least once a year.

This routine, year-round use is described by experts cited in the report as 'blanket use'.

Environmental charity River Action's head of campaigns Amy Fairman said: 'We fully support the call for this ban.

'These flea treatments are among the most toxic chemicals entering our rivers, yet they continue to be sold with little thought for where they end up.

'Pet owners deserve clear, informed advice before using these products so they can understand the potential impact on rivers and wildlife.

'Our freshwater ecosystems are already under immense pressure, and biodiversity needs protecting from avoidable sources of chemical pollution too.'