Can the UK close massive deficit with China?
To say that the Chinese market represents a huge opportunity for British companies has traditionally been like saying that there would be no water shortage if only we could get the salt out of seawater cheaply - it's been true in theory, and hugely tricky to do in practice.
The crude statistics of our trade in goods and services with China tell you most of what you need to know: in 2009 we sold £8.7bn of tangibles and intangibles to China, and we bought three times as much, £25.8bn, from the Chinese.
It's true that UK exports of goods to China rose 44% in the first eight months of 2010 to £4.5bn, but our current account deficit with China is by far the largest deficit we have with any trading partner.
And although over 10 years our sales of goods and services to China have increased by a seemingly healthy 4.6 times, imports have risen by a far greater multiple, 6.6 times.
No British lectures
That said, with the arrival in China of a significant proportion of the British cabinet (chancellor, business secretary, education secretary, energy secretary and prime minister are all coming), as design or luck would have it this may be the moment for British companies to generate significant job-creating sales in China.
When I interviewed Vince Cable in the British Ambassador's Beijing residence earlier today (not too shabby a crib, as my son might say), he insisted that the bilateral deficit with China doesn't bother him - he prefers to see trade in the round, in a multilateral sense.
And Mr Cable insisted he would not be picking up the widespread concerns in the US that the Chinese currency is undervalued: Mr Cable said he had not flown all this way to lecture the Chinese that they should allow the yuan to appreciate against the dollar.
... while in France
So what is the point of this huge ministerial and business mission to Beijing?
Well I suppose that in a China where state-owned enterprises represent a massive proportion of the economy, it probably helps that British ministers are seen to be batting for non state-owned British companies: although I do wonder whether the current sophisticated crop of Chinese ministers and officials genuinely believe that the likes of BP and Rolls-Royce dance to a Whitehall tune.
It's not altogether surprising that when the Chinese president, Hu Jintao, visited France last week, the French president Nicolas Sarkozy claimed the countries had struck £14bn of commercial deals, rather more than Mr Cameron will flaunt: some would say that there is an incestuous relationship between the French state and commerce which is almost Chinese.
Unsustainable economic model
But it's reasonable to be optimistic that UK exports to China will increase because - as the Chinese government concedes - China's economy needs to be reconstructed pretty fundamentally, if the official target of growing at around 8% per annum is to be continued in a sustainable way.
Putting it in the crudest possible terms, the Chinese population of more than 1.3 billion people has to consume more relative to the size of their economy.
Even the Chinese authorities concede that China's current economic model - of growth generated by huge domestic investment and massive net exports helped by an exchange rate that is forcibly held down below where it ought to be - cannot be sustained forever.
Our debt = their surplus
There is of course no consensus between China and America on the urgency of the necessary reforms.
But there is some consensus that the Great Recession of 2008-9 was at least in part caused by the madness of a global economic system in which the net importing western nations, like the US and UK, have taken on crippling indebtedness as the corollary of China's (and Germany's and Japan's) huge surpluses (the dispute between China and America is whether the propensity to borrow created the surpluses, or vice versa).
On that view, the Great Recession was just the first shock - and global economic stability will be illusory unless and until the net exporting nations and net importing ones find an orderly way to achieve balance (which is what the G20 heads of government will agonise about at their summit in Korea at the end of the week).
The Chinese Good Life
Certainly the Chinese seem in little doubt that the massive increase in domestic investment they engineered to restart the economy after it stalled at the end of 2008 is only a short-term fix: it'll seriously hurt the banks which financed the investment unless a market for the output of all the new productive capacity is created at home and abroad.
There is also a much more basic way of seeing the inevitable reconstruction of the Chinese economy towards consumption.
Here in China there is a growing sense that the good life should be about more than just working all hours to supply the trinkets demanded by indebted Brits and Americans.
The Chinese want some cake too.
At the high end of the income scale, they want Beamers and 'S'-class Mercs. Between just June and September, Mercedes sold 41,000 vehicles in China, one in eight of all its car sales, a rate of growth of 140%.
Colossal spending gap
But for most Chinese, it's about much more basic needs.
That is already being reflected - according to the US investment bank Goldman Sachs - in around a third of Chinese GDP growth coming from spending by the household sector in 2010 and 2011, up from 28% three years ago.
In fact Goldman's China economist, Yu Song, thinks the current strength of consumer spending here might mean it delivers 40% of GDP growth.
But that is still about 25 percentage points below the share of consumer spending in the British and American economies.
So the magnitude of the money potentially available to western exporters is colossal.
As Jim O'Neill of Goldman tells me, even now just the growth in China's imports every year is equivalent to the entire output of the Greek economy, or around £250bn.
That's a lot of whisky, and aero-engines and chocolates that could be made in Britain and sold in China.
Update 0800, 8 November: The US has now conceded that there'll be no agreement at the G20 summit on quantitative targets for current account surpluses and deficits.
Which means that there'll be no hardening up of the deal made last month by G20 finance ministers to avoid - in some nebulous sense - long-term current account surpluses and deficits.
That is not a great shock given that the great exporters of Asia, South America and Europe (a big hello to Germany and China) regarded numerical targets as bonkers.
And they opened a new front of criticism against the US, by asserting that the Fed's $600bn of money creation through quantitative easing is degrading the US dollar.
Against that background, it will be fascinating to see what the Chinese commerce minister Chen Deming tells me about the prospects for the G20 Summit, when I interview him tomorrow.