Calling for a "grown-up conversation" on the subject, David Cameron has said that net immigration to Britain is too high.

The Conservative leader used his first major speech on the issue on Monday to pledge a cut in the figure under a Tory government.

He claimed demographic pressures made it essential to form policies to curb immigration and the growth in the number of households as more people choose to live alone.

Cameron was addressing the Policy Exchange think-tank following projections from the Office for National Statistics last week that Britain's population will rise from 60 to 71 million by 2031.

"Britain's population is set to grow rapidly," he said. "That growth will come mainly from a combination of higher life expectancy and higher net immigration. 

"At the same time we are seeing another significant demographic change: the growth in household formation, partly caused by the increasing atomisation of our society. 

"These trends will put pressure on our national infrastructure - particularly in key areas like housing, public services and transport – and on resources like water and energy."

He argued that while he is not against immigration itself, "these demographic changes, and the pressure they will cause, will make it more difficult for a Conservative government to deliver its vision of opportunity, responsibility and security".

"And so it's essential that we also develop a coherent strategy, and implement joined-up policy, to address population growth and the atomisation of our society," Cameron concluded.

"Of course we should recognise that in an advanced, open economy there will be high levels of emigration and immigration. But what matters is the net figure, which I believe is currently too high.

"So we need policy to reduce the level of net immigration - and we also need to bring together policy issues from housing to skills; planning to immigration control; the family to border control, into a coherent long-term population strategy."

Cameron promised that the party will set out a series of policies over the coming months aimed at reducing the country's reliance on immigrant labour by improving the UK skills base.

He also said the Tories are to address the problems of family breakdown, which is causing the number of people living alone to increase.

However immigration minister Liam Byrne said Cameron's speech appeared to be "a re-hash of the same old platitudes".

"He talks about a cap on numbers but this is a smokescreen if he refuses to name a number, especially when his small print seems not to touch European Economic Area nationals, overseas students and dependents who made up 80 per cent of British incomers last year," Byrne added.

And Liberal Democrat home affairs spokesman Nick Clegg said: "This is yet more fantasy politics from David Cameron.

"He tries to appear reasonable whilst pandering to the right wing in his own party, and claims that immigration numbers should be cut without having the faintest clue as to how that would happen.

"Does David Cameron have a magic number in mind or does he seriously think that immigration can be turned on and off like a tap?"