Global banks and international bond strategists have been left stunned by revised ONS figures showing that Britain is £490bn poorer than had been ­assumed and no longer has any reserve of net foreign assets, depriving the country of its safety margin as Brexit talks reach a crucial juncture.

A massive write-down in the UK balance of payments data shows that Britain’s stock of wealth – the net international investment position – has collapsed from a surplus of £469bn to a net deficit of £22bn. This transforms the outlook for sterling and the gilts markets.

“Half a trillion pounds has gone missing. This is equivalent to 25pc of GDP,” said Mark Capleton, UK rates strategist at Bank of America.

Making matters worse, foreign ­direct investment (FDI) by companies is plummeting. It fell from a £120bn surplus in the first half 2016 to a £25bn deficit over the same period of this year.

The apparent resilience of FDI flows shortly after Brexit was an illusion: the spending that took place in late 2016 had already been committed earlier. The big devaluation since late 2015 ­automatically improved the UK’s net asset profile enormously but clearly not enough. The supposed surplus has gone up in smoke. It implies that the UK’s underlying position going into the referendum was much weaker than anybody realised. The concern is that the external forces supporting sterling and gilts are all in doubt as major central banks tighten policy and drain global liquidity.