Before too long, one pound is going to be worth one euro. Next year might not be the year we see this, but it might well be the year we start accepting its inevitability.
Rather than ask what factors will drive sterling down to this psychological level, let's flip the question on its head and ask what there is to hold it up. The answer is: not a lot.
Certainly not the economic fundamentals. The UK's economy is over-dependent on financial services, retailing and property. That's why Gordon Brown is desperate to get banks lending to each other again. The City of London represents a big chunk of the nation's economic activity and the government can ill afford to see thousands of unemployed bankers - even if it fills the rest of us with a warm schadenfreude.
It's why consumers are being urged to 'get spending again'. Instead of saving or investing, we're supposed to spend money we haven't got on stuff we don't need, most of it imported, in order to get shops back on their feet.
Such spending habits are - or rather, were - encouraged by the feeling of wealth and security engendered by ever-rising house prices. That's why every movement in the property market is micro-analysed by a cottage industry akin to Kremlinology. Other countries simply do not carry on like this. They make stuff, and export it. What do we export, apart from whisky, guns and pop music?
These imbalances are graphically illustrated by the UK's swelling current account deficit, which is now equivalent to 3 per cent of GDP. In the past, this has been financed by capital inflows from the Middle East, Asia and Russia. But China's savings are more likely to stay at home in future, while the falling oil price has curbed the spectacular spending of Russians and Arabs - as the recent failure of Robin Ellis Construction, "London's poshest builder", illustrates.
Monetary policy has propped the pound up in the recent past; interest rates in the UK have been higher than those in the eurozone, as the Bank of England tried to keep a lid on inflation. But following recent dramatic easing, UK base rates are among the lowest in the world and could go lower still. So that crutch has been well and truly kicked away.
The next supporting factor to disappear will be oil. Since the late 1960s, the UK has been a net exporter of crude oil. Not any more. We are now a net importer, and we'll import more crude as our domestic oil reserves dwindle. With a fiscal regime that seems designed to drive explorers into the arms of the Norwegians, it's hard to see what's going to reverse that trend.
Lastly, a weaker pound isn't fresh news. The most recent downward lurches have been just the latest in a long decline. Look at the chart of the pound versus the deutsche mark since the late 1950s. It tells its own story. In the mid-1980s, Margaret Thatcher persuaded the Sultan of Brunei to buy pounds in order to prevent sterling reaching dollar parity. Who will help Gordon Brown keep the pound away from euro parity?
