By Kris Jepson
ITV News Tyne Tees was given exclusive access to the raids in Berwick, which saw 11 people arrested in total.
This included eight men, aged 20, 33, 35, 38, 39, 47, 51 and 54, and three women, aged 29, 41 and 53. All were arrested on suspicion of conspiracy to supply Class A drugs, and all have suspected links to Merseyside.
In Merseyside, police arrested three males, aged 16, 17 and 18, all on suspicion of conspiracy to supply Class A drugs.
The officer in charge of the raid said "this sends a crystal clear message to anybody involved in County Lines operations" in the North East that Northumbria Police will deal with them "robustly".
Working with Merseyside Police and the North East Regional Special Operations Unit (NERSOU), 12 warrants were carried out in the North East and North West.
Named Operation Eclipse, five of the warrants took place at properties in Berwick, which police believe have been taken over by the Merseyside gang using a practice called "cuckooing".
County Lines gangs exploit vulnerable people in rural towns like Berwick and "cuckoo" their homes in order to carry out drug deals.
During the raids officers also seized a quantity of drugs, drugs paraphernalia and a number of mobile phones suspected to be linked to County Lines.
This crime is commonly where criminal networks expand their operations from urban areas to more rural locations and smaller towns.
Drug dealers will typically use a single phone line to facilitate the supply of Class A drugs, often resorting to violence and intimidation to protect the line.
Often, County Lines will involve the exploitation of vulnerable people, including children and those with mental health or addiction problems, at all points of the drug supply routes.
Edge North East is an organisation based in Newcastle that supports vulnerable young people who have been caught up in County Lines.