By bizn_fun 
Concerns have also been raised about vulnerable borrowers having their credit limits increased without asking.
Tom Richardson, an academic who researches debt and mental health, says his own experience left him shocked. He has bipolar disorder, and about a year ago, during what he describes as a severe manic episode, he walked into his local guitar shop.
“I just came in for a bit of a look. There wasn’t anything in particular I wanted,” he says.
However, by the time he left the shop, he had bought a guitar, a ukulele and another piece of equipment. He then went online and bought more, putting everything on his credit card.
“Electric guitar, speakers, guitar pedals, a guitar amp, a trumpet, some sort of bongos, some pads for my computer music equipment,” he recalls buying.
“When you’re manic, when you’re impulsive, it just doesn’t feel like real money.”
By the time the episode ended, he says he was close to his card’s £7,000 credit limit. With help from family, he started to pay the balance down and told his bank, Santander, about his medical diagnosis.
Six months later, Santander increased his credit limit to £9,000.
“I was trying to do the sensible thing and reduce the debt,” says Tom, “and the default response was to offer me more credit. It was mind-boggling.”
His experience is not unusual, research suggests. Four in 10 credit card holders across all lenders were offered a limit increase in the past year, with little distinction made between those struggling and those not, a survey by debt charity StepChange found.
Santander told us that when Tom first signed up to his credit card, he opted in to automatic credit card limit increases. The bank said it monitors “customer spending closely against past transactions in order to spot any unusual and unaffordable behaviour”.