Consumer helplines have sounded a warning after Britons ran up their highest level of new debt in November for nearly seven years, with the month’s borrowing on credit cards, loans and overdrafts hitting more than £1.25bn.

National Debtline and StepChange said the figures from the Bank of England showed a worrying rise in consumers’ reliance on credit, and warned they expected a rush of people seeking help when the first credit card bills of the year started to arrive.

Banks and credit card companies have been jostling for business with offers to attract new customers: loan rates have plummeted while balance transfer deals on credit cards have become increasingly generous.

The £150bn UK credit card industry is to come under investigation this month by the Financial Conduct Authority over accusations of aggressive marketing after the watchdog suggested it had been pushing “payday loans with plastic”.

The £1.25bn net increase in unsecured borrowing during November was the biggest rise since February 2008, when Northern Rock was nationalised as the credit crunch took hold. It was the third month out of five that consumers had taken on more than £1bn of new debt.

More than £980m was taken out in loans and overdrafts during the month, sharply up from the monthly average of £728m over the previous six months. Credit card lending fell to £269m, from £399m in October, but remained above the average for the previous six months.

The Bank of England said over the course of three months unsecured lending had grown at its most rapid pace since October 2005, and in November was up 6.9% compared with November 2013.

The figures show that at £168bn – more than £5,800 per household – the total outstanding unsecured debt remains some way below the peak reached in September 2008 when UK consumers collectively owed £208bn alongside their mortgages.

However, there has been a marked change in behaviour as the economy has recovered: in nearly every month for the four years to September 2012 consumers paid off more than they borrowed, with banks reining in credit limits and restricting loans and overdrafts, but since then the trend has reversed with almost every month seeing increased borrowing.

Howard Archer, chief UK economist at IHS Economics, said the surge in retail sales around Black Friday was probably linked to the increase in borrowing – retail experts IMRG estimated £810m was spent online during the promotional day – but he added there were also likely to be other factors behind the rise in debt. “Relatively high consumer confidence means people have become more prepared to borrow in recent months,” he said.

“It also may well be that a significant amount of people have recently been borrowing more due to the squeeze on their purchasing power coming from extended low earnings growth.”

The shadow consumer minister, Stella Creasy, said the UK had a “massive looming personal debt crisis” and many households were being forced to borrow to fund living costs. “They’re not buying big fancy TVs and posh holidays – they are borrowing to cover the gap between what they earn and what they need to pay for each month,” she said.

Creasy said there was a “big gaping hole at the heart of our economy” being fuelled by borrowing, and tackling problem personal debt needed to be a political priority.

Joanna Elson, chief executive of the Money Advice Trust, the charity that runs the service, said: “While most people will be able to cope with this extra borrowing, we are concerned that many households will have overstretched – particularly over the Christmas period.”

The chief executive of the debt charity StepChange, Mike O’Connor, said the figures “point to a worrying rise in people’s reliance on credit”. He added: “The economy is growing and there is some wage growth but it is very marginal and millions are living on a financial precipice leaving them vulnerable to financial shocks and strains.

“The prospects are for more austerity and economic prospects are uncertain. People may turn to credit as the only accessible way to try and plug the gap. If and when we see an interest rate rise, many more people will struggle.”

The charity dealt with 50,000 clients in January last year and expects the figure to be higher this year.

Before Christmas, research by R3, the trade body for people working in the insolvency sector, found that a quarter of adults were expecting to take on debt to pay for their celebrations, with 50% planning to use an existing credit card, 24% using overdrafts, and 14% saying they would use a store card. Payday loans, new credit cards and loans from family were among other sources of credit people expected to turn to.

In the competition for borrowers, banks have focused on balance transfers, with increasingly long interest-free periods offered as an incentive to move debt between lenders. Just before Christmas Barclaycard started offering 35 months at 0%, and and this week Halifax and Lloyds Bank launched 34-month deals – but such deals involve upfront fees of 2.5%-3%.

Personal loan rates have also plummeted: two years ago the best-buy £5,000 loan had an interest rate of 7%; now the same amount can be borrowed at 4.9%, meanwhile on a £10,000 loan you can pay just 3.9%, against 5.4% in 2013.

Andrew Hagger of financial website Moneycomms said he expected to see a flurry of new offers over the coming weeks. “January and February is always the period of consolidation, with people sitting down and sorting out their finances. I’m sure we will see some more banks cutting loan rates and offering new deals.”

While unsecured credit market increased in November, the Bank of England’s figures showed a slowdown in mortgage lending. The number of mortgages approved for house purchases fell to a 17-month low of 59,029, below the average of 63,191 recorded over the previous six months and down by more than 22% on the 76,574 offered in January 2014.