The leaders of eight trades unions today hit back at Rachel Reeves, Labour's new work and pensions spokeswoman, for pledging to be "tougher than the Tories" on cutting the welfare bill, and accuse her of "bashing the victims of failure".

In a letter to the Observer, the union bosses say it is "pathetic that politicians compensate for their failure to build an economy that provides adequate jobs" by implying that some of those who are out of work want to stay on benefits.

"Unemployed people are perfectly capable of assessing what is in their best interests, without threats," says the group, which includes the general secretaries of several major unions, including Mark Serwotka of the Public and Commercial Services Union, Michelle Stanistreet of the National Union of Journalists, and Steve Gillan of the Prison Officers' Association.

Last Sunday, in an interview with this paper, Reeves, who was promoted to shadow work and pensions secretary in Ed Miliband's recent reshuffle, said that Labour would be "tougher" than the Conservatives in slashing welfare costs. The long-term unemployed would be offered a job under a government scheme, and would lose their benefits if they refused it. She said that no one should expect to be able to spend a life on benefits under a Labour government. Her comments angered some on the left of the party, who saw them as aping Tory language on welfare claimants.

Labour taunted the coalition over the lack of growth in the first half of this parliament, but its own difficulties on the economy will probably be highlighted this week when the chancellor, George Osborne, points to new evidence that the UK has "turned a corner", with official figures expected to show that the recovery is gathering pace.

When the Office for National Statistics publishes its first estimate of GDP in the third quarter of the year on Friday 25 October, City analysts expect it to reveal growth of 0.8% – an improvement on the 0.7% recorded during the previous three months, and stronger than the independent Office for Budget Responsibility expected in March, when it forecast 0.6% growth for 2013 as a whole.

Some economists are projecting an even more robust performance, perhaps 1% or more, after a series of upbeat business surveys. Rising consumer confidence as the housing market has begun to thaw in many parts of the country, and the end of the recession in the eurozone, the UK's major market, has helped firms to feel more optimistic about their prospects.

Labour is likely to respond by stepping up its argument that with wages still rising much more slowly than inflation, very few families are feeling the benefits of economic recovery, because of what Miliband has called the "cost of living crisis".

The shadow chief secretary to the Treasury, Chris Leslie, said: "To catch up all the lost ground since George Osborne became chancellor, we need to see 1.4% growth every quarter between now and the next election. We need action to secure a stronger recovery that sees rising living standards for the many, not just a few at the top."The latest official figures on the labour market, published on 16 October, showed that a record 29.87 million people are now in employment in the UK, but average wages in the three months to August were only 0.7% higher than a year earlier, while inflation was running at 2.7%.

The contrast between paltry pay increases and the rocketing cost of living was underlined as British Gas became the latest utility company to announce a price rise, pushing up bills by more than 10%.