Opposition politicians have suggested that Tony Blair's government is failing to deliver on its key promises.

As Blair becomes the longest continuously serving Labour leader, shadow chancellor Michael Howard said the government's record was one of failure.

And Liberal Democrat leader Charles Kennedy warned that ministers now appeared to be running out of steam.

Howard said that while Labour had put up taxes, the promised "world class public services" had failed to materialise.

"Despite the back-slapping and boasting, under Labour a million people remain stuck on waiting lists, a third of eleven year olds leave primary school unable to read, write or count, and our transport system is in gridlock," he said.

"Britain deserves a government that delivers. Labour love to talk about their investment, but where are the results?"

And the Lib Dem leader said that Blair's place in history was far from certain.

"The great reforming governments of the twentieth century - those of Asquith, Attlee and Thatcher - introduced changes which influenced the direction of our country for many years," Kennedy said.

"Tony Blair started out in office claiming a zeal for radical change - like devolution and reform of the House of Lords. It is clear that zeal has largely run out.

"On the big long-term issues facing the country now - further constitutional change, our place in Europe and environmental policy - the prime minister has shown a remarkable timidity.

"Tony Blair's best days may well be behind him."

But despite the criticism, the prime minister has remained determined to press ahead with his New Labour agenda.

"Modern social democracy is what today's Labour Party is about and must continue to be about," Blair has said.

"There are real challenges, of course, that lie ahead for the government and for the country, but I would say after six years of office Britain has the lowest inflation, interest rates and unemployment for decades; half a million children have been lifted out of poverty; there has been record investment in the National Health Service and schools, which is improving results significantly; crime is falling, and Britain is stronger in the world.

"So there is an enormous amount still to do. But those achievements are real, and I believe will be sustainable."