He said Labour's handling of the financial turmoil was based on myths and that the economy would be more resilient through "Conservative responsibility".

At the Glasgow Science Centre he said: "This recession was triggered by a credit crunch and it is now vital that we unblock credit and get money flowing through the veins of our economy, back to businesses and families."

He added: "I believe we need to move away from an economy that relies too heavily on the narrow shoulders of finance and housing to drive growth.

"We need to move towards science, more hi-tech services, more green technologies, more engineering, more high-value manufacturing."

Mr Cameron set out to debunk three "myths": that economic downturn was caused by America, that the way out was to increase spending and that government could borrow without limit.

He said: "In Britain our Government thought the good times would never, that boom and bust would never end. We entered the downturn the least prepared country in the developed world."

He said Britain had built up a mountain of private debt, adding: "The consequence – we are forecast to have the biggest recession of any major economy."

But the Tory leader said there should be "no blank cheque" to save the economy.

He said: "I believe that it's an irresponsible choice because it risks taking a road which will lead to economic ruin. What we're responsible for borrowing now will saddle this generation and the next with a level of debt that could take a decade or more to pay off – which means instead of building schools or hospitals and getting more police on our streets it means spending priorities will have to shift to service our gargantuan debt."

Earlier yesterday Mr Cameron called for greater protection for people in debt who were at risk of losing their homes or having bailiffs "steal" their possessions.

On GMTV he said no-one with less than £25,000 of unsecured loans or bills should be forced to sell their house in order to make repayments.

He added that in the current economic climate the Government should also scrap plans to allow debt collectors to break into properties to reclaim goods.

Mr Cameron said: "The Government are trying to change the law to allow bailiffs to break into your home and take your possessions.

"We think that is wrong. They should not be allowed to break into your home and effectively steal your possessions. In this recession, lots of people are going to get into terrible trouble.

"There are problems at the moment with people who get their homes repossessed not because they are not keeping up payments on their mortgage but because they have credit card bills or other unsecured loan bills. That is wrong."

But Justice Secretary Jack Straw insisted none of the powers were in force – and would not be if they threatened to have any "adverse effect" during the credit crunch.

"None of the provisions of the legislation to which David Cameron is referring today have been implemented," he said.

"Indeed, four weeks ago I asked one of my Ministers, Bridget Prentice, to review the enforcement provisions of the Tribunals, Courts and Enforcement Act.

"In particular, I will not agree to the implementation of measures on charging orders until
I am satisfied that they will not have an adverse effect during these difficult economic
times."