A Conservative government will introduce new controls on state spending and borrowing, replacing Gordon Brown's "busted" rules with a more rigorous framework, George Osborne, the shadow chancellor, will pledge today.

The opposition party will seek to convert its criticism of Labour's alleged financial irresponsibility from an economic argument into a mainstream issue for voters. Mr Osborne will use a speech attacking Mr Brown over fairness, a theme traditionally seen as Labour territory, to argue that the rising national debt is a moral, as well as economic, issue.