Temporary Detective Chief Superintendent Gordon Lang said James Allen was arrested after an off-duty officer spotted him in South Leeds this morning and urged the public to keep sending in information on the case.
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The shadow chancellor appeared to differ from his leader, who had been initially reluctant to blame the Kremlin for the ex-spy attack.
The Foreign Secretary said the Kremlin's tit-for-tat expulsion of 23 British diplomats would only impact Vladimir Putin's compatriots.
Sunday will be bitterly cold with snow for most.