Government borrowing fell slightly in May, according to the Office for National Statistics (ONS), but it still failed to meet analysts expectations.
Compared with May last year, borrowing dropped £400 million to £9.7 billion. But economists had forecast borrowing would fall to £9.5bn in May.
The ONS also revised down borrowing for the full financial year to March to £74.9bn. But borrowing so far in the current financial year is actually £200m more than at the same point last year.
Public sector debt rose to £1.606 trillion, or 83.7% of the UK's GDP.
The Office for Budget Responsibility forecast the government would borrow around £20bn less in the 2016/17 financial year than last year.
Ross Campbell, public sector director of the ICAEW, accused George Obsorne of taking his eye off the economic ball while the EU referendum has taken centre stage.
He said: "The impending EU referendum vote has contributed to an uncertainty that has resulted in a sluggish UK economy, therefore it was imperative that the Chancellor put public sector finances at the top his priority for May 2016. An increase of £0.2bn in public sector net borrowing in the current financial year-to-date, when compared with the same period in 2015, illustrates that he has done quite the opposite and has taken his eye off the economic ball.
"Whatever the result on Friday morning, whether we remain in or leave the European Union, it is vital that government devises a comprehensive and rigorous strategy to kick-start a faltering economic recovery."