I suspect there's a long list of things which are not election issues but which should be. On this list should be: what to make of the fact that the UK's current account deficit last year was 5.5% of GDP, the biggest peacetime deficit since at least 1816*?
First, let's put this into a context. One of the big developments of recent years has been the near-disappearance of the non-financial corporate sector's financial surplus. Since 2011, it has fallen from £69.9bn to £1.1bn, its lowest level for 14 years. This could be tremendously good news. It means that capital spending has risen relative to retained profits - which could be a sign that the dearth of investment opportunities is fading.
However, there's one notable effect this hasn't had. It hasn't led to a big decline in government borrowing.
The point here is simple. Financial balances MUST sum to zero: if one sector is a net lender, another muct be a net borrower. In the past, swings in the corporate sector's surplus have been mirrored by swings in the government's deficit. For example, corporate surpluses in the early 90s and late 00s were accompanied by government borrowing, and corporate deficits in the late 80s and late 90s were accompanied by government surpluses. To put this in more familiar terms, strong capital spending means a strong economy and hence buoyant tax revenues.
However, the fall in the corporate sector's surplus recently hasn't greatly reduced government borrowing. Instead, its counterpart has been an increase in the current account deficit: as the UK domestic sector (which includes households and financial companies as well) has gone from surplus to deficit, foreigners' financial surplus has risen.
Hence the question I began with: what to make of this?
One possibility is that this shows that the UK lacks capacity in tradeable goods and services. As capital spending and hence economic activity generally has picked up, we've sucked in imports. Our incomes have, in effect, leached overseas rather than to the taxman.
One could therefore argue that we do indeed have a structural government budget deficit, in the sense that there's a big deficit even when the private sector is running a normal financial balance.
This provides a better justification for a tight fiscal policy than the Tories are offering. Such a policy means - given the inflation target - a low path for interest rates which should weaken sterling and so boost competitiveness; think of the standard Mundell-Fleming story. Sadly, this argument is weakened by the Meese-Rogoff puzzle. But one could revive it: to the extent that the external deficit/foreigners' surplus is the counterpart of the government deficit, maybe austerity is needed to reduce the current account deficit and so prevent a disorderly adjustment in which sterling collapses.
There is, though, another interpretation. Maybe the exogenous variable is foreigners' desire to save - due to the Asian savings glut and government and private sector retrenchment in the euro area. If foreigners want to save, someone has to borrow. And that someone has been the UK government.
Financial markets seem to believe its the latter: falling index-linked yields and a strong pound tell us as much.
Which brings me to a hunch. This might be changing. Signs of a recovery in the euro area have been accompanied by a fall in the UK's trade deficit, the biggest part of our current account deficit. This could mean that the foreign sector's surplus is falling. If this happens as the same time as the domestic sector continues to run a deficit, then the government deficit will shrink.
Given that what passes for economic policy debate is often just an application of the post hoc ergo propter hoc fallacy, this might mean that the next government - whoever it is - will be able to claim success in reducing borrowing.
* Based on B.R.Mitchell's British Historical Statistics. Data since 1830 are in this Excel file from the Bank of England.