Dr Simon Harding, of Middlesex University London, interviewed illegal and legal dog owners as well as gang members as part of his research.
The research found that dangerous dogs are being bred by young men as a business asset in drug deals, debt collection and for their gang image.
A 16-year-old boy told him: "It's not just a dog, it's a half bull mastiff and half pit bull. I'll probably get another - we are looking to breed it - and we would get about £2,000 per dog."
Another boy, 17, said about pit bulls: "People know that if you are breeding you are making money from them."
More top news
In a tweet on Saturday, the US president didn't give a reason for his absence but said he wished"everyone well and have a great evening".
Weather conditions remain wet and windy through the weekend.
Mr Banks has given Ukip leader Paul Nuttall an "ultimatum", saying if he is not made chairman he will stop supporting the party.