Seventeen kilograms of Class A drugs, three firearms and a 'large quantity' of cash have been recovered in today's police raids in Sheffield.
Police have estimated the value of the substance- which appears to be heroin although testing has not yet confirmed this- to be at least £500,000.
This estimate is based on the substance being prepared for street dealing but depending on the purity police said the value could be up to £1million.
The force made 12 arrests and recovered many illicit items - mainly from four warrants carried out in the Burngreave area of Sheffield as part of Operation Duxford.
Operation Duxford aims to improve links with the local community, identify and tackle criminal activity, and protect vulnerable people living in communities affected by crime.
The intelligence-led operation began early this morning and will continue late into the night.
Temporary Superintendent Simon Wanless said: "It's been better than we could have hoped."
He added: "Should we not be doing this all the time? Yes we should, and we will. For me it's an element of making this day to day activity and not a special occasion."
Operation Duxford is set to ahead in Doncaster, Rotherham and Barnsley in the next three months, returning to Sheffield in March.
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