The UK borrowed £34.1bn in December, the highest figure for that month on record.
The UK's national debt is now £2.13 trillion, worth 99.4% of GDP, a level not seen since the early 1960s.
Responding to the figures, Christine Jardine, Liberal Democrat Spokesperson for the Treasury, said:
"These unprecedented borrowing figures lay bare the exceptional challenges we face this winter due to Covid-19. People are struggling and we must not leave anyone behind.
"While the vaccine offers hope we cannot lose sight of the fact that millions of people are still struggling to stay afloat.
"Furlough must be extended, the three million excluded from all Covid support brought under the Government's umbrella and struggling small businesses given immediate relief if we are to avoid thousands of closures.
“Right now, the Chancellor needs to worry about people not numbers and fulfil the pledge to do whatever it takes in the March budget.”