The money was seized in Belle Vue, Wakefield, yesterday under the Proceeds of Crime Act as dozens of police officers swooped on homes across the city in early-morning raids.

The cash can be confiscated by the courts if police can prove it has been made through crime.

Operation Grassland is one of the biggest clampdowns of its kind ever seen in West Yorkshire and is expected to net up to 100 major drug dealers in the Wakefield district – which would be a record number of arrests.

Many of the raids took place after tip-offs from members of the public and police urged more people to phone in with information about dealers and other criminals.

Police also seized seven cars and quantities of various illicit drugs, including crack cocaine.

Police said the operation, which began Monday, was aimed at dealers and serious organised criminals.

Some of the dealers have been operating around schools in Wakefield, said Det Chief Insp Mick McDermott.

Thirty nine arrests have been made so far but more will follow, police said.

So far the operation has covered Agbrigg, College Grove, Kettlethorpe and Lupset.

Chief Supt Marc Callaghan, divisional commander for Wakefield, said: "The community are vital in our fight against crime and this operation demonstrates that we will listen to their concerns and we will take firm action against criminals operating in our local communities.

"By reporting their concerns to their Neighbourhood Policing Teams, the people of Wakefield have shown that they are no longer prepared to tolerate drug dealing on their doorsteps."

He added: "We always act on information but sometimes people don't see immediate action as we have to make sure the information is genuine and we have the best chance of securing evidence."