British anti-terrorist police arrested seven people during early morning raids in London and Manchester in England, and Glasgow and Edinburgh in Scotland.
Six men and one woman were detained under the Terrorism Act 2000.
Police said two men were arrested in the Scottish capital Edinburgh, a man and woman were arrested in Glasgow, one man was arrested in the Manchester area, and two men were arrested in London.
Britain has been on heightened alert since the discovery of traces of the deadly ricin poison in a London apartment last month, following which anti-terrorist police made a string of arrests.
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But Deputy Chief Constable Tom Wood of Lothian and Borders police said no dangerous substances had been found in the latest raids.
AFP