Economists expect official figures to show Chancellor George Osborne is on track to beat official forecasts for government borrowing.

The Office For National Statistics will release its figures on Tuesday, and analysts expect them to show the government had a surplus of around £6 billion in January - which is typically a bumper month for tax receipts.

This would put the Treasury in line to rack up a deficit for the full 2011-2012 financial year of around £120 billion - undershooting the Office for Budget Responsibility forecast of £127 billion.

January's figures are key because they are the last to be revealed before the Budget, which will be published by the Chancellor on March 21, and will give a final chance to judge whether the Government is on track to reduce the annual deficit.

The figures also come shortly after ratings agency Moody's put the UK's AAA credit rating on negative outlook.

Howard Archer, chief UK and European economist at IHS Global Insight, said: "January normally sees a net repayment on the public finances as it is a key month for tax receipts.

"A modest year-on-year improvement in the public finances is expected in January as a result of the fiscal measures that have increasingly kicked in over the past year. In particular, spending cuts should now be having an impact on the public finance figures."

However, national debt is still high. December's data revealed the UK's debt mountain smashed through the £1 trillion barrier for the first time in history.

The grim milestone, equivalent to some £16,400 per person in the UK, is equal to 64.2% of the country's gross domestic product.

The total may ease back to less than £1 trillion thanks to the expected surplus in January, but is likely to grow again in the coming months.

Archer said looking further ahead, the Chancellor is likely to struggle with future targets for borrowing as the economy struggles. The Treasury is forecast to post a £120 billion deficit in 2012/13.

He said: "It seems inevitable that the public finances will be increasingly pressurised over the coming months by muted economic activity eating into tax revenues and pushing up unemployment benefit claims."