By Mark Davies BBC News Online political reporter

A fresh wake-up call to the Tories has been delivered by the party top brass as David Willetts told Conservatives to "stop twitching at the net curtains as society changes".

The shadow work and pensions minister, who announced new proposals to introduce "lifetime savings accounts", said his party had failed to understand the power of the changes it had introduced while in government.

"We've got to recognise and understand social change. There's no point twitching at the net curtains as society changes around us

David Willetts

And as the party attempts to cast itself as the voice of the vulnerable and shed its "nasty" image, he declared: "The Tory war on single parents is over."

Tory chairman Theresa May told representatives at the Bournemouth conference on Monday that the party had to change and embrace all parts of society.

Mr Willetts, who has toured the UK as he forges his policy plans, said the Thatcher and Major governments had transformed the UK through the liberation of the economy.

"Yet we who delivered all these changes appeared not to understand the very social forces we had unleashed," he said.

"We've got to recognise and understand social change. There's no point twitching at the net curtains as society changes around us.

'Maze'

"We must engage with society as it is today. Then we can put all our efforts into the problems that need to be tackled."

Iain Duncan Smith wants his party to look more tolerant

Attempting to press his party's "one nation" credentials, Mr Willetts said the Tories were proud of their reputation as the party of national defence, enterprise and the countryside.

But he said the party also needed to be proud to be the party of social reform.

He vowed that a Conservative government would free families from the "maze" of Gordon Brown's tax credits to create "a simpler, more straightforward" system.

He said he would also work for a reduction in red tape in relation to savings, introducing a new Lifetime Savings Account which would lift restrictions on when cash could be withdrawn from pension funds.

He said: "It will enable everyone to build up their own personal pot of savings to draw on as they wish. This is a radical proposal. It tackles a problem at the heart of our savings culture.

'Battle'

"We want people to enjoy the independence that comes from building up their own personal pot of savings."

On single parents, a target for Conservative attacks in the past, he said: "Let me make it absolutely clear: the Tory war on lone parents is over.

"The real battle is to support and strengthen the nation's families. They come in all shapes and sizes. Too often they are struggling in a hostile environment.

"When they are not being ignored, they are being blamed. When they are not being blamed, they are being taxed.

"Our approach will be very different. We'll support them and value them and above all, we'll back them."