(Reuters) - British government borrowing over the last six months was over 10 percent higher than in 2013, official data showed on Tuesday, giving Chancellor George Osborne a tough task to meet his full-year borrowing goals.

Osborne aimed in March to reduce Britain's budget deficit by more than 10 percent over the following 12 months, and Tuesday's figures suggest he has little scope to offer sweeteners to voters before national elections due in May.

Borrowing for September alone was 15.3 percent higher than a year earlier at 11.8 billion pounds, the Office for National Statistics said. That compared to economists forecasts for it to hold roughly steady at 10.5 billion pounds.

For the first six months of the financial year, public sector net borrowing, excluding state-controlled banks, was 58.0 billion pounds, 10.3 percent higher than in 2013.

Last month's data showed that borrowing between April and August was 6 percent higher than a year earlier.

Exact comparisons between the government's budget plans and actual borrowing are difficult. Since last month, the ONS has been using a new method for calculating the headline measure of British public borrowing.

Under the old measure, public sector net borrowing excluding financial sector interventions, stood at 12.6 billion pounds in the month of September, up 14.5 percent from a year earlier.

Borrowing on this basis was forecast in March to fall to 5.5 percent of gross domestic product in the 2014/15 tax year from 6.6 percent in 2013/14. Revisions to GDP and other changes mean that on the new measure, 2013/14 borrowing is now estimated to have been 5.7 percent of GDP.

Deficit reduction has been the central economic policy of the Conservative/Liberal Democrat coalition government since it took power in 2010. Weak growth in 2011 and 2012 has meant that it will not achieve its original plan to largely eliminate the deficit by 2015.

The government has said that the extra borrowing so far this year is due to an uneven pattern of tax receipts in 2013, and that the differences would even out before the end of the financial year.

However, last week the head of the government's budget watchdog said that there appeared to be a bigger problem as greater numbers of people in work were not bringing the expected increase in income tax revenues.

Tuesday's data showed that revenue from income tax and employment insurance contributions in September was 2.3 percent higher than a year ago, while for the year to date it was up by just 0.5 percent.

The government's budget watchdog forecast in March that income tax revenue would rise by 7 percent this year.

Total government revenue was down by 0.4 percent in the first half of the tax year, and the only bright spot was receipts from property and share transaction taxes, which were up by more than a third on the year.

While Britain's economy has grown faster than average so far this year, and unemployment is falling rapidly, wages are growing more slowly than inflation and the government has raised how much people can earn before they start to pay tax.

Public sector net debt excluding state-controlled banks totaled 1.451 trillion in September, matching June's record high of 79.9 percent of GDP.