The office of National Statistics revealed that public sector net borrowing, the government's preferred measure of the public finances, in September stood at 5.2 bln stg, up on last year's expectations of 4.7 gbln nd expectations of a modest improvement to 4.5 bln. That was the highest September deficit since records began in 1993. A spokesman for the statistics office said the main reason behind the rise was an increase in net investment on things like schools and hospitals. However he conceded that net investment is a volatile component of government spending. The deficit over the first six months of the fiscal year is slightly better than last year's but is way below that projected in the budget. Net borrowing over the first half of the year stands at 22.9 bln stg against 23.6 bln at the equivalent period last year. In his budget earlier this year, Chancellor of the Exchequer Gordon Brown predicted that PSNB over 2005/6 would improve to 31.9 bln from the 36.8 bln recorded in 2004/5. Brown, who has already conceded he got his economic growth projections wrong, publishes his latest forecasts in next month's pre-budget report. Once the net investment component is stripped out, the figures make for better reading for the Chancellor. The deficit on the current budget, which strips out government investment, during September stood at 3.4 bln stg against 3.8 bln last year. Brown uses the current budget when assessing his 'golden rule' of balancing the budget, excluding investment, across the economic cycle. On a cumulative basis, the current budget deficit in the first half of the year has improved to 14.6 bln stg from 17.6 bln last year. In July Brown was accused of fiddling on the golden rule. Brown announced that the current economic cycle began in 1997, two years earlier than previously thought. As a result, the Treasury is able to include an extra 9 bln stg of surpluses to offset the deficits recorded over the last couple of years. Even though the change in the start of the current economic cycle means the golden rule is more likely to be met, economists still expect tax increases of around 10 bln stg sometime over the next few years to bring the budget into balance over the next economic cycle. Elsewhere in today's release, an alternative, but more volatile, measure of the public finances worsened too. The public sector net cash requirement in September was 11.8 bln stg, up on last year's equivalent of 10.9 bln, and above expectations of a 10.0 bln shortfall. The September requirement was the highest since records began in 1984. The main reason behind the rise was an increase in interest payments on gilt issues. The statistics office also said net debt at the end of September stood at 440.0 bln stg, which is equivalent to 35.5 pct of GDP. Brown's second fiscal rule, the sustainable investment rule, requires net debt to be below 40 pct of GDP.