Labour's post-modern approach to commitment and marriage is bad for family policy, David Willetts said last night.

Unveiling the second of a series of major policy pre-conference statements, the shadow work and pensions secretary declared that Conservatives were "rediscovering society".

He accused Tony Blair of embracing a "post modern world of shifting loyalties and thinner relationships", delivering a stinging attack on a morality-lite third way.

Singling out Downing Street's "moral neutrality" on marriage - a policy area on which the Cabinet is split - Willetts argued that Blair was out of step with the nation.

In an intellectual riposte to new Labour's modernism, the Havant MP - dubbed "two brains" - took on the empty philosophy behind the third way, linking it to Blair's struggle against "old" party ideology.

"A theory of the end of permanent attachments could well appeal to Blairites in the process of remaking their own party. If they were busy detaching their party from its roots, we should not be surprised that they embraced a theory which said that was what the rest of us were doing as well," he told the Policy Exchange think tank.

"But it is a misunderstanding of Britain.

"Blair's attempts to reconstruct Britain around this theory of jostling, shifting, temporary lifestyle choices is out of touch with the reality of the lives and aspirations of most British people."

Willetts told the centre right audience there was no place for family commitment in the third way vision.

"You won't find much about parents and children in the Third Way. They do not fit in because they bring with them obligations that can't be shed."

"This may be one reason why Blair's government has found it so difficult to develop any sort of coherent family policy."

The question of strong social ties, Willetts stressed, was key to "our understanding of society".

"The Blairite pundits claim that we as a nation are abandoning marriage."

"It is relegated to just another lifestyle choice, alongside many other supposedly equally popular and widespread ways of living," he claimed.

Downing Street's aversion to family commitment contradicted "evidence from across society [showing] how resilient and widespread marriage is as an aspiration".

"We are more demanding, you might even say consumerist, in our approach both to jobs and to relationships.

"We have high expectations and we spend much longer trying to get the decision right.

"But after a much longer period of experiment and mobility than in the past most of us do make that decision," Willetts insisted.

"After we search we settle. That is because there are deep sources of human satisfaction which come from long-term commitments and trust."

In contrast, he said Conservatives understood "the power of commitment, trust, and attachment that come with the institution of marriage and we support it".

"We believe that it is usually best for children to be raised in a two-parent home, Willetts concluded.

"I believe that people have a powerful urge to be social, to share, to commit to others. They want to build a stable environment for their children. They want to create something worthwhile. These are profound human needs reflected in the way our society has been shaped."

"And at a far more profound level it is the yearning for attachment to a partner, embodied above all in the institution of marriage. The problem is that all too often it is politicians who have created an environment which weakens these ties," he said.