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Intelligence chiefs believe it is a growing possibility after reports that radioactive material was stolen from hospitals in Syria.
One senior intelligence source said: “The dirty bomb is a crude but effective device. You basically strap a radioactive material to an explosive and when it detonates, it will cover a wide area with relatively low-grade but dangerous material.”
Meanwhile, armed police, undercover experts from the Special Reconnaissance Regiment and plain-clothed units from the SAS are being ordered on to the streets.
Rings of steel spring up around Christmas markets

“The dirty bomb is a crude but effective device”
Senior intelligence source
And SAS snipers will watch over city centres on New Year’s Eve ready to take out any terrorists attempting attacks on revellers.
Britain’s most senior spy Andrew Parker believes London and other major cities including Manchester, Birmingham and Glasgow, could be threatened.
It is understood that potential targets include Christmas markets and major shopping centres.
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British agents have also briefed business leaders and the heads of supermarkets to make sure their staff remain vigilant and report any suspicious behaviour.
Mr Parker, head of MI5, also told ministers during a briefing on security that they have an unprecedented number of UK-based “persons of interest”.
A source added: “Parker was quite clear that his organisation could not stop every terror attack and it was only a matter of time before jihadis struck again.”