The Treasury will increase the rate of a tax on bank balance sheets to maintain the 2.5 billion pounds ($3.9 billion) of revenue it aims to collect each year, media reports said on Saturday.

Chancellor George Osborne would announce the rise in his autumn budget statement to parliament on November 29, the Guardian newspaper and Sky News said in unsourced reports.

Some banks have been shrinking their balance sheets to comply with tougher capital adequacy rules, by shedding riskier assets and reducing borrowing.

That meant the Treasury needed to raise the rate of the levy to keep to its revenue target, Sky News said.

The levy, introduced in January, is currently charged at a rate of 0.075 percent on bank debts, with a lower rate charged for longer-term debt and an exemption for ordinary customer deposits.

As well as raising revenue, the levy is designed to encourage banks to reduce their short-term funding to help avoid a repeat of the 2008/9 financial crisis.

The rate could rise to around 0.1 percent, Sky News said.

A Treasury spokesperson declined to comment on the reports.

(Reporting by Tim Castle and Fiona Shaikh; editing by Andrew Roche)