The Bank of England has sounded the alarm on the U.K. housing market.

The central bank has announced two new lending rules and standards for mortgages in the U.K, with the goal of, "[limiting] the risks to financial stability and the economy from a significant increase in the number of highly indebted households."

The first is a stress test of a borrower's ability to pay a mortgage if rates rise, and the other limits how many of a lender's mortgages can be more than 4.5 times a borrower's income.

Last week, the U.K.'s Office for National Statistics reported that housing prices increased 9.9% in April, up from an 8% increase in March. And the London housing market was up significantly, with annual home prices rising 18.7%.

The BoE said mortgages represent 80% of household debt in the U.K., but added that it, "does not believe that household indebtedness poses an imminent threat to stability."

Here's a chart showing the annual increase in home prices.

This chart shows the increase in U.K. home prices since 2002.

And this break down by region shows the change in the London market, which is exploding.

These new rules from the BoE come about two weeks after BoE Governor Mark Carney suggested that interest rate increases could come sooner than the market expects. A change in interest rates would make those who hold variable rate mortgages particularly vulnerable.

The BoE said it is "prudent" to insure against housing market risks, positioning the rules as preventing a problem rather than reacting to one.

But Baroness Jo Valentine, chief executive of London First, told the BBC: "If anyone thinks these tighter rules on mortgage lending will somehow make London prices more reasonable then they are mistaken."

The U.K. housing market is undeniably booming, but whether this boom has led to a bubble-like situation that will end badly remains to be seen. The Bank of England is clearly paying very close attention.