SINCE the Brexit vote of June 2016, the pound has lost 15% of its value against other currencies. Traders have sold sterling because they fear for the economy’s prospects. Yet some see an upside to the slump. With products more competitive abroad, the argument goes, the economy will “rebalance” away from consumer spending towards export-led growth. Last month Liam Fox, the international-trade secretary, spoke of the “increasing demand for home-grown summer essentials”, boasting about British exports of swimwear and ice-cream. Unfortunately, however, sterling’s depreciation is likely to go down as one of the least successful in history.

For most of the past three centuries, Britain has run a trade surplus. Its biggest, worth 6% of GDP, was in 1881, at the height of the British empire. However, in recent years Britain has run large trade deficits.

Past depreciations have helped reorient the economy back towards export-led growth. In 1967, when Harold Wilson devalued the pound against the dollar, assuring Britons that the “pound in your pocket” had lost none of its value, a jump in exports followed (see chart). The conditions looked good for a repeat this time around. Despite protectionist rhetoric from Donald Trump, world trade has grown decently in the past year.

Yet exporters have responded meekly to the depreciation. The real-terms value of exports has risen only slightly. In April to June the trade deficit was just a squeak below its five-year average. The impact of sterling’s depreciation has been underwhelming for a few reasons. For one thing, firms are locked into global supply chains and rely heavily on foreign inputs. Half the components in a “British-made” car come from abroad. If exports rise, so do imports. The economy is also highly geared towards high-value-added stuff like pharmaceuticals. Buyers of these goods and services are insensitive to price changes. Not all industries fit this mould, notably tourism. Dollars buy more rides on the London Eye than before. In June visits by foreigners (including businesspeople) were up by 7% year on year. Yet visitors seem to be economising: their overall spending in real terms is no higher than before. Optimists maintain that the benefits of a depreciation take a long time to filter through. Firms need to get finance together and seek out new markets to exploit their new competitive advantage.

The case of Dr Fox’s ice-cream industry, however, suggests that exporters are in no rush. Though export revenues have risen, this largely reflects the fact that with a weaker pound a given quantity of foreign-currency sales leads to higher sterling revenues. In the first half of 2017 firms exported about the same quantity of ice cream (600m scoops, by our reckoning) as in the same period the year before. Firms seem to be using sterling’s weakness simply to bank bigger profits, rather than to move into new markets.

It is a similar story across the private sector. Profitability is near record highs yet investment is stalling. Last year non-financial firms stuck an extra £74bn ($96bn) in their bank accounts, by far the largest figure on record. Firms’ tentative behaviour should be a wake-up call for ministers, who expect them to lead the charge of a reorientation of British trade away from the EU after Brexit.

Following a period of stability in early 2017, sterling has once again started to slide downwards. On August 29th it hit €1.08, its lowest level against the euro since 2009. There remain few indications, however, that an export boom is around the corner. It turns out that devaluing your way to prosperity is not easy.