At a time of jittery markets and uncertain prospects around the world, the U.S. and Britain have still managed to end the year posting the strongest economic growth among major advanced countries, helped by consumer spending.

But a warning sign has emerged in the U.K, whose growth now stands on a far flimsier footing: Households are once again spending more than they earn. Among developed countries, only Canada is in a similar place. Both summon memories of an imbalance that brought the global economy real pain in the latest financial crisis.

And once again, high home values are mainly to blame.

Rapidly rising property prices are fueling a belief among homeowners that they can bulk up on debt. This is a risky move because money in real estate can’t be quickly drawn upon in times of need, which means small economic slumps are more prone to be transformed into larger declines in consumption if people become overly worried about their cash needs. A collapse in house prices could also leave another generation underwater.

Since reaching a postcrisis low in 2012, British house prices have risen by 21% and are back at 2006 levels after discounting inflation, according to the Bank for International Settlements.