TODAY is a big day for Tony Blair. The big aim of his second term of Government is delivery in terms of improving public services.

The big problem is that decades of under-investment have left everything, from our schools to our hospitals to our railways, in need of big money.

Mr Blair's big stumbling block is his belief - a belief apparently reinforced by his Chancellor Gordon Brown who holds the purse strings - that the public wants Continental levels of service but wants to pay American levels of tax.

The only way to reconcile these two contradictory objectives is to find ways of bringing new money into the public services. Today, in his speech to the TUC conference, Mr Blair will attempt to explain that this is not creeping privatisation of the NHS or our education system.

Yesterday, Trade and Industry Secretary Patricia Hewitt took some welcome steps to protect public sector workers who are transferred to the private sector. But today, Mr Blair needs to do more than correct anomalies. He has to explain his big idea because, so far, the concept of public-private partnership seems to have slipped out of a vacuous General Election campaign without being fully fleshed out.

He cannot expect the public or the unions - who, in the absence of an Opposition, are doing their best to hold the Government to account - to fall in silently behind his plans because there are so few examples of the partnership working. The privately-run National Lottery has endured plenty of embarrassments; here in the North-East, there's the suspicion that privately-financed hospitals will cost more in the long-run and not improve levels of service; in the country as a whole the chaos of the privately-operated railway system fills no one with hope for the success of future similar experiments.

Mr Blair also has to provide a big vision. The public service ethos is so important to nurses and teachers who, in return, do not expect to earn the megabucks of big business - but how does Mr Blair see that ethos squaring with the aims of the private moneymen who will be looking for huge profit, large salaries and massive dividends for their shareholders?

Mr Blair's big aim, of improving services, is unquestionably the right one. He must now persuade us that he is on the right path.