The governor of the Bank of England Mark Carney has promised to take action to combat the rapidly growing buy-to-let market.
Mr Carney said he was concerned about the level of lending to landlords. Speaking to the Financial Times, he said: "There are a number of things happening ... we are watching it closely and we will take action."
There are currently around 1.7 million buy-to-let mortgages in the UK, which have pushed up the total value of mortgages by around 16%
He explained that there is a greater risk that landlords may sell properties at the same time if house prices fell. The Bank of England's Financial Policy Committee (FPC), led by Mark Carney, made a similar warning in September.
At the time, the FPC said the growing buy-to-let market poses a significant threat to the stability of the UK economy. Since the Committee's warnings, the Chancellor George Osborne has announced that stamp duty will be increased for people buying a property that is not for their own, regular residence.
But the higher stamp duties are not due to come in until the new financial year in April, which has led to concerns that landlords could rush to purchase properties before then.