Clive Chamberlain from Dorset Police Federation is among those taking part in the march. Officers from every police force in the country are taking part in the protest in London.
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The Government had provided up to £150,000 a year to support the language since 2003, but have now withdrawn all funding.
A bird that features on Cornwall's coat of arms is making an "amazing" comeback after disappearing from the county in the 1970s.
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