UK unemployment has broken through the 2.5 million mark for the first time since the Labour government came to power, after the jobless total jumped by 43,000 in the three months to February.

At 2.502 million, the number of people out of work is at its highest since the last three months of 1994. The jobless rate is now 8%, its highest since 1996.

The number of people classed as economically inactive also reached record levels, according to data from the Office for National Statistics. Economists warned that the figures underlined the fragility of the UK economy.

But there was also brighter news, with the ONS reporting a surprisingly large drop in the number of people claiming unemployment benefit. The claimant count fell by 32,900 to 1.54 million in March, a much larger decline than the City had expected. This follows a revised fall of 40,100 in February, which was the sharpest drop since June 1997.

Colin Ellis, European economist at Daiwa Capital Markets Europe, said it was "pretty remarkable" that the claimant count had now fallen for four of the last five months.

The ONS data showed an 89,000 drop in the number of people in employment in the three months to February. This took the UK active workforce down to 28.824 million. Ellis said that a large proportion of those people are now in education, which could indicate problems in the future.

"The vast majority of that number are now students – consistent with people trying to gain qualifications while the labour market remains weak, ahead of any potential upswing in the economy. But with private sector job creation still a long way off, the risk is that, while these students do not currently boost measured unemployment, trouble is just being stored up for further down the line," Ellis warned.

The number of people classed as economically inactive rose by 110,000 to 8.16 million, the highest level since records began in 1971. Long-term unemployment, which measures those out of work for more than a year, increased by 89,000 to 726,000.

Howard Archer, chief European and UK economist at IHS Global Insight, said that the claimant count could be lower than expected because some people are "either unable to claim benefits or choosing not to".

Archer dubbed the data a "real mixed bag", and argued that it is too early to predict that unemployment has peaked.

"The mixed latest data reinforces our belief that it is premature to call the all-clear on the jobs front, despite recently improved economic activity and the overall resilience of the labour market through the economy's travails. Indeed, we suspect the labour market may well be somewhat erratic in the near term at least, with some months of unemployment gains and some of losses," said Archer.

Both main political parties seized on the mixed data as campaigning for the 6 May general election continued. The Conservative party said the rise in unemployment proved that Labour was wrong to be planning to raise national insurance.

Theresa May, the Conservative's work and pensions spokeswoman, told Sky News that the employment figures were "grim news for tens of thousands of families up and down the country".

But the government argued that unemployment would have smashed through the 3 million barrier without its efforts to support those out of work.

"We have to be clear. There are still a lot of people who are being affected by the recession, and a lot of people who need help," said Yvette Cooper, the work and pensions secretary.

Liberal Democrat Treasury spokesman Vince Cable said the unemployment data showed the weakness of the UK economy.

"Without a strong and concerted plan of action to support jobs and businesses, the fall-out from the recession will be with us for years to come," Cable warned.