The reclassification by the Office for National Statistics (ONS) of the Royal Bank of Scotland and Lloyds Banking Group as public corporations will be a big help to the efforts of the chancellor, Alistair Darling, to limit fiscal red ink. The banks’ underlying profits will be booked as public sector income, significantly reducing net borrowing.

At first sight this looks odd since the banks suffered a combined operating loss before tax of £49.0 billion in 2008 and may remain in the red in 2009. ONS guidance, however, indicates that the profits definition to be used will exclude dealing/investment losses, credit impairments and goodwill write-downs. Profits before these deductions were a combined £27.7 billion in 2008. (The ONS figure could be lower because of other adjustments, e.g. excluding undistributed income of foreign subsidiaries.) RBS and Lloyds are to be included in the public sector from 13 October 2008.

The chancellor is widely expected to announce a large upward revision to his public sector net borrowing forecast of £118 billion in 2009-10 in next month’s Budget, reflecting a much deeper recession than projected by the Treasury last November. The average independent projection is £128 billion, according to the Treasury’s monthly survey of forecasters. The inclusion of the banks’ profits, however, implies that Darling could announce little or no increase.

The effect, of course, is entirely artificial: although not included in public borrowing, the losses suffered by the banks are real and have been reflected in the value of the government’s shareholdings. With no improvement in the public sector’s true financial position, the classification change does not create additional fiscal “room for manoeuvre”.

The ONS previously announced that the reclassification of the banks would boost public net debt by between 70 and 100 percentage points of gross domestic product from 47.8% currently.