Tony Blair's pre-election outing to the West Country was an eventful affair.

First, to remind him of the troubles on the railways, his train was late.

Then, on his way into a further education college to meet students, he was pelted with fruit by a group protesting against the bombing of Iraq. One ripe tomato hit him in the back.

He almost had a further close encounter with fuel protestors: a dozen-strong convoy of tractors and lorries was prevented by police from picketing his speech.

Eventually, some 20 minutes behind schedule, he began his speech at the council offices in Bristol, afterwards inviting questions from his audience.

Staff shortages

The theme was Labour's record in investment in the public services, which he has already billed as one of the main planks of the election campaign.

Michael Portillo: The government is vulnerable

But despite the huge sums promised by Chancellor Gordon Brown to health and education, and the commitment to boost police numbers, a number of awkward problems have appeared in recent months.

Several schools are reporting a severe shortage of teachers, and a few have warned that they may have to cut lessons and send children home.

There are similar recruitment problems in the NHS: ministers have admitted that many of the extra staff proposed in the National Plan will have to come from abroad. The police have had similar problems.

One sign of the times is the spate of glossy television advertisements designed to underline the importance society places on the roles of teachers and police officers.

Poster blitz

Opposition parties are well aware of this possible weak spot in Labour's armour.

Conservative leader William Hague and his shadow chancellor, Michael Portillo, launched their new poster campaign the same day, its general theme being "You've paid the tax - where are the services to show for it?"

William Hague: Thousands ask me "Where's the money gone?"

Mr Hague claimed that an average family is paying an extra �670 in tax compared to 1997, and he highlighted the current problems in schools, hospitals and on the railways as evidence that the money has not been well spent.

Labour rejects that criticism. Social Security Secretary Alistair Darling told BBC Radio 4's the World at One that sustained investment in the public services would be at risk if the Conservatives were to win the election.

He argued that services would have to be cut to provide the funds for the tax-cuts promised by Mr Hague.

But that may not stop public sector pay from becoming an election issue.

Ministers have responded to teacher shortages with emergency measures to attract and retain staff in difficult areas. There's been talk of special contracts and "golden handcuffs".

However, the bulk of teaching staff w ill not benefit. The National Association of Head Teachers said that a minimum of 5% extra would be needed to satisfy the union's members, rather than the 3.3% they will receive from April.

According to Andrew Dilnot of the Institute of Fiscal Studies, every 1% on public sector pay across the board would cost a billion pounds.

Some now believe that the government will, nonetheless, have to relent in its determination to hold down general pay levels.