Uniformed officers, detectives and specialist search units entered six yards across four counties at 10am in a co-ordinated move codenamed Operation Symphony.
The officer in charge said it was one of the largest enforcement phases mounted by his force in response to a crime that posed a danger to the public.
Metal theft is one of the fastest-growing crimes in the country, driven by high prices, with offences costing the UK £770 million pounds annually.
The hunger for scrap has been responsible for damage to buildings, the rail network and communications infrastructure, as well as the disappearance of public works of art.
Detective Chief Superintendent Brendan O'Dowda, the head of Thames Valley Police's force intelligence unit and specialist operations, was in charge of the operation.
He said: "We see cars being stolen to be scrapped, manhole covers from roads, power and telecoms cabling literally ripped from under roads and railway lines and copper earthing stolen from electricity substations.
"You just wouldn't believe the lengths that some of those thieves will go to to get some cash. They will steal crematorium plaques and plaques from war memorials.
"This crime literally shuts down schools and railway networks and truly isolates people across villages and communities, especially more vulnerable people.
"This is not a victimless crime."
He added: "It represents a threat to public safety, it threatens our national infrastructure and has a considerable societal impact - that's not to mention the threat to the public purse."
Many people, while not technically vulnerable, utterly depended on electricity or telecoms connections and could be hugely affected by metal thieves, he said.
Others were left bereft when memorial plaques at crematoria and cemeteries were stolen, as well as statues.
People in the Cheshire town of Warrington were horrified recently when a plaque remembering two boys killed in an IRA bombing in the town was torn from a wall.
In Maidenhead a statue commemorating two boys who died in a skiing accident was stolen. It was found by police but not before it had been broken into pieces ready to be melted down.
Det Chief Supt O'Dowda said: "I regularly receive letters from victims of crime, saying what are you doing to tackle the issue of metal theft.
"At the moment we are doing a lot and the message to the public is we are doing something about it and we do take it seriously."
Places raided this morning were :
* A4 Metal Recycling Ltd, Beenham Industrial Park, Beenham.
* A1 Group, Silver Birches, Highland Ave, Wokingham.
* Smiths of Bloxham, Milton Road, Bloxham, Oxon.
* TR Rogers & Sons, The Metal Yard, Nuneham Courtenay, Oxon.
* AG Evans Ltd, Chesham Roadd, Tring, Herts.
* A Smiths & Sons, 91 Parkview Road, Uxbridge.
The task force will seize the business' records for forensic examination, while other officers will pore over the stock in the yards to try to identify any stolen goods, from cabling to lead roof flashing and metal artworks.
Officers were likely to be at the various sites for a number of days due to the size of the operation.
Det Chief Supt O'Dowda said in addition to the yards, officers were also at eight "associated premises", although he would not be drawn on their specific locations.
Today's raids were the culmination of many months of painstaking investigation involving a large number of Thames Valley officers, working with colleagues from other forces, including British Transport Police, as well as local authorities, the Environment Agency and the British Recycling Agency.
The aim will be to disrupt the metal theft network by targeting those who trade in stolen items.
"The vast majority of businesses are very well run and work within the law and legislation but many are not," said Det. Chief Supt. O'Dowda.
"At best they turn a blind eye to metal theft and at worst, talking about the more unscrupulous, they actively encourage the trade of stolen metal, without giving any consideration to its origin or the impact the theft has had on the communities.
"Our message is - for those businesses who choose to operate responsibly and within the law, we will work with you, and those who don't, we will use our collective energy to target you at every opportunity until you comply with the legislation."
Behind the scenes senior officers in the Thames Valley were working with their counterparts from other forces and representatives from the Association of Chief Police Officers (ACPO) to lobby Government to review the current legislation addressing metal theft.
"At the moment we work to the Scrap Metal Dealers Act of 1964, which is outdated," said Det Ch Supt O'Dowda.
"We want to see tighter regulation and requirements around production of photo id and also for dealers to have to retain the scrap metal in its original format for some time. But we are where we are."