Radiological material found at terror probe house
The Metropolitan Police said "small traces of radiological material" had been detected during a counter-terrorism operation in Bedfordshire.
Specialist officers have been searching a house in Caddington, near Luton, after suspicious substances were found earlier this month.
A 31-year-old man from Bedford has been arrested on suspicion of terrorism offences and remained in custody.
Cdr Dominic Murphy, head of the Met's Counter Terrorism Command, said officers had found "no evidence that any form of 'dirty bomb' has been or was being constructed".
"During the searches over the past few days, some very small traces of radiological material have been detected," he added.
"I want to stress that at no stage was it identified as being at a level that would pose any kind of risk or harm to the public.
"I can also reassure the community that further inquiries and analysis has confirmed that the substances containing these traces are found in everyday use - such as material found in smoke alarms, or those historically used in paints for luminescent watch dials."
The Met said it did not believe there was any risk to local residents or the wider public.
An investigation at the property was first launched by Bedfordshire Police on 6 May when items, including a number of suspicious substances, were found.
Police said the 31-year-old man was arrested on suspicion of causing explosions likely to endanger life and possession of Class A drugs, and was bailed while investigations continued.
On Monday, following additional searches at the address, the investigation was subsequently passed to the Met's Counter Terrorism Command due to the "nature of items found".
Bedfordshire Police confirmed a controlled explosion took place, which residents said was at the back of a preschool.
On Tuesday, the suspect was additionally arrested on suspicion of possession of articles for terrorist purposes.
Police said he was detained under the Terrorism Act and a Warrant of Further Detention was obtained on Thursday at Westminster Magistrates' Court.
It means he can remain in custody until 21 May.
Police said specialist officers continued to search the property.
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