How do you turn £500 billion (€735 billion) of public spending into a soundbite? How do you differentiate your spending plans when the vast bulk of them are exactly the same as those of your political opponents?

These are the far-from-trivial tasks facing the main political parties, each of which has produced an economic manifesto that strives to improve public service and to protect the NHS, while at the same time promising to be both radical and different.

All this definitely without raising taxes, according to the Tory party; no tax rises, but not so sure about national insurance if you are Tony Blair. Meanwhile, the Lib Dems promise higher taxes on anyone earning over £100,000 a year. Labour has tried, with much success, to keep the focus of the election campaign on the broader economy, while the Tories have kept the infamous "dog whistle" issues at the centre of their strategy.

Imported from Australia, this new tactic seeks to identify key issues that have immediate appeal to certain types of voters. In terms of economic policy, two such issues have been council tax - particularly for the elderly - and pensions. The "new" partnership of Blair and Brown has, in contrast, sought to remind voters about the government's economic record and the threats to economic stability posed by anybody other than themselves.

The broad brush features more prominently in Labour's manifesto than the dog whistle, with Gordon Brown effectively relaunching his previously published spending plans as manifesto promises.

But the great boom in spending growth is over, with a commitment to stabilise spending as a share of GDP essentially from the current fiscal year. This is to be achieved while maintaining borrowing rules and without tax rises: outside experts disagree, with the Institute for Fiscal Studies suggesting that Gordon Brown will have to raise taxes by £11 billion if his self-imposed debt limits are not to be breached.

The Tories are promising to reduce spending as a proportion of the economy, mostly by implementing a tough efficiency drive for the public sector. This is where it all starts to get murky.

Two recently published audits of public finances have revealed large potential savings in expenditure to be made from that old favourite, the elimination of waste. The James report came up with a figure of £35 billion, which the Tories have promised to split up via an £8 billion cut in borrowing, a £4 billion tax cut and £23 billion in extra public spending. The Gershon report, by contrast, has promised only £21 billion of saving, but this has largely been factored into existing government sending plans.

Whether it's £35 billion or £21 billion, these savings have to come from somewhere: both parties promise large cuts in the civil service, and the usual war on waste. Naturally, all sides take great liberties with the data, revealing their own ignorance of arithmetic, let alone accountancy, and displaying a breathtaking contempt for the ordinary voter: it is clear that few politicians believe that anybody can follow any of this debate.

Claims and counter-claims have flown between the parties, with accusations about expenditure cuts and double counting.

The simple truth is that the single distinguishing factor between Labour and the Conservatives is the growth of public spending.

Labour promises a growth rate of around 3 per cent, the Tories 2 per cent; Labour wants to stabilise spending at 42 per cent of the economy, the Conservatives 40 per cent. From these relatively simple goals flows all the confusion. The £4 billion tax cut promised by the Tories is the only such promise by any party, but is trivial by any standard - less than the average forecast error of public sector borrowing.

The Tories say you can increase spending, cut taxes and reduce borrowing: Labour argues that this verges on fraudulent. As a matter of arithmetic, the Tories could be right, but it all depends on how fast you assume the economy grows (remember those commitments expressed as a percentage of GDP). Neither side will achieve its efficiency savings: every government in living memory has been elected on a promise to eliminate waste in the public sector. Few have delivered.

The most peculiar aspect of the fiscal battle is that neither the Conservatives nor the Liberal Democrats seems capable of pointing out that we have witnessed an astonishing increase in public spending over the past four years and we have very little to show for it.

The Tories, in particular, seem to be scared witless about the possibility that someone might accuse them of favouring cuts in public spending.

Labour's spending plans are taken as the bottom line by most parties and only tinkering at the edges is to be permitted.

Failure to be courageous and simply to make a stand for smaller government will cost the Tories whatever chance they had in this election. Nobody is willing to make the case that just as higher spending resulted in no change in public sector service standards, so lower spending can have exactly the same effect, but with the happy by-product of lower taxes. More than one commentator has observed that the most remarkable feature of the two main manifestos is that a neutral observer would not be able to identify which was Labour or Conservative.

The old divisions of left and right have gone, as have the visions - and visionaries - that used to light up previous election campaigns.

Chris Johns is an investment strategist with Collins Stewart. All opinions are personal.