By Daniel Hunter

The Chancellor George Osborne will announce his aim to prevent future governments from overspending by maintaining a budget surplus when the economy is growing.

Osborne's annual Mansion House speech will outline his plan to limit governments to a balanced budget in "normal" times, a change first proposed in January.

With concerns over the national debt, which has doubled since the financial crisis, this plan would legally prevent future governments from spending more than they receive in tax revenue when the economy is growing.

The Office for Budget Responsibility (OBR), an independent watchdog, will be responsible for policing the new rules. The OBR is also likely to have the power to decide when the government should be able spend more than it is taking in revenue, for example when the country is in a recession.