As the Conservative lead tumbles, so falls the pound, and the price of UK government debt. Apparently, traders are worried that the election will come and go, and we won't know who's in charge of No 10.
But, when you think about it, the markets might have good reasons to sell the pound, even if Labour or the Conservatives win a clear victory.
How so? Well, consider, first, the other reasons why the markets might be down on the pound. (Yes, I do know that explaining daily exchange rate movements is a fruitless exercise, but I've started now so I guess I have to finish.)
There were some pretty dovish remarks last week from the governor of the Bank of England and some of his colleagues on the Monetary Policy Committee - that could lead traders to think interest rates will stay low for even longer than previously thought.
Other things equal, if rates are expected to be lower than before, then that will push down the pound.
Thursday's dire investment figures for the final three months of 2009, and the news on Friday that investment and exports had played no part in the recovery so far, could also leave investors worried about the health of the economy from now on. That's why sterling did badly at the end of last week.
But it does seem that politics and the deficit are at the centre of today's moves. After all, some of the latest economic news - like this morning's manufacturing purchasing managers' index - was quite good.
The line is that markets fear uncertainty. And a hung parliament, in a country that is not accustomed to them, sounds like a very uncertain prospect indeed.
As a factual matter, you could say this fear is ungrounded. It turns out that seven of the 10 most ambitious programmes of budget cuts in the Organisation for Economic Co-operation and Development in the last 40 years have been achieved by coalition governments.
There is also the fact that Britain's third largest party - which could be the kingmaker in a hung Parliament - has a respected economics spokesman, Vince Cable, who is somewhat more hawkish on the deficit than the chancellor.
However, if you are a sterling trader, none of that really matters.
Even if a minority Conservative government, or a coalition, could probably pass a tough emergency budget, the important point is that you can't count on it. The shadow of uncertainty could hang over the UK for weeks.
But here's the funny thing. Imagine this weekend had brought news of a massive widening of the gap between the Conservatives and everyone else - to the point where a Tory election victory looked all but in the bag.
What would that same trader have done then? It's quite possible he would have sold the pound as well.
Why? Because if he knows anything about George Osborne it is that he would run a tighter fiscal policy than Labour, and he would start that tightening right away. Other things equal, that should push down the pound.
As the shadow chancellor explained very clearly in his Mais Lecture last week, more rapid budget cuts need not endanger the UK's recovery. And the main reason he doesn't think so is that it would, other things equal, mean lower short and long-term interest rates, and a lower - sorry, more competitive - pound.
Mr Osborne didn't exactly say: "vote for us, vote for a lower pound". But last year his staff were keen to point journalists in the direction of an article by a Goldman Sachs economist, Ben Broadbent (see my post from 14 September), making the argument that tighter fiscal policy need not hurt UK growth.
The central part of that analysis was that exports would take the place of the lost government spending, because budget cuts and relatively looser monetary policy would lower the value of the pound.
This argument may or may not be right. But, as I say, the Conservatives were quite happy to cite it in support of their policies.
We have to assume they would not be unhappy with a lower pound. Indeed, if the pound fell on the back of an Osborne emergency budget, you have to imagine they would welcome it.
And what about Labour? What if traders had woken up this morning and found Gordon Brown 10 points ahead?
Well, on the basis of the previous argument, you might expect me to say the pound to go up. After all - wouldn't a "loose" Labour government drive up long-term bond yields (ie long-term interest rates) - and encourage the Bank of England to tighten sooner as well? And wouldn't these higher interest rates spell a higher pound?
Well, maybe. If you're an academic economist. But it might not be the first instinct of many investors in the markets, many of whom have gone back to associating Labour with economic instability and possibly higher inflation as well.
In fact, you might expect them to sell on a big Labour lead as well. After all, Labour needs a recovery built on exports as well. And even with the dramatic depreciation we've already had, there's not much sign of those exports coming through.
So, there might have been political and economic reasons to sell the pound - whatever today's polls had said. For today at least, that is what is known in the trade as a one-way bet.