Britain's 30-somethings should take to bed to solve the pensions crisis, the Tories have said.

Shadow work and pensions secretary David Willets has called for a shift in the age structure of society.

In a pamphlet for the Centre for European Reform he argues that Britain needs to produce more babies to stave off a demographic time bomb.

By boosting the birth rate in Britain Willetts argues the long term savings deficit will be reduced as the size of the UK workforce expands.

The pensions crisis has not been caused by people living for too long, he argues.

"The problem is that there are not enough young workers coming along behind," Willetts claimed.

"After the baby boom of the 1950s we have had the baby bust.

"Europe's real demographic crisis is not longevity but birth rates."

Rather than encouraging migration or longer working lives, the solution is to provide incentives for more couples to reproduce, Willetts said.

"Europe faces a birth-dearth," he added.

"Nobody wants to force women to have more children than they wish.

"But we have created an environment in which people are having fewer children than they aspire to.

"The evidence is very significant...it is the societies with the most traditional roles for women (and men) such as Italy, which have the lowest birth rate."

The government needs to engender a raft of family-friendly policies which would encourage the trend, the Conservatives are set to suggest.

"It is societies where women - and men - can combine work and children that have higher birth rates," Willets argued.

"This means we need a family-friendly agenda that goes way beyond the conventional plea from state-sponsored childcare.

"What really does matter is... a greater diversity of jobs in a more flexible labour market [and] easy access to finance enables couples to create a home and raise children."