Private equity firms that take over companies can be bad for jobs, but they can also be good, according to a new report from The Work Foundation.

The report, Inside the dark box: shedding light on private equity found that private equity firms that take over companies and bring in new management teams are likely to cut jobs and depress employees' wages. On the other hand, where an existing management team helps take a company into private equity, you end up up getting more jobs and the impact on wages is smaller.

The report, however, is fairly scathing about the kind of work practices that private equity seeks to put in place:

"There are reasonable grounds to be sceptical about whether PE improves life at work markedly. The price that is paid for the extensive use of Performance management and incentivisation may be an increase in stress, anxiety about job security, and damage to morale and the levels of trust between managers and employees. Elements of the employment relationship that have been identified as aspects of 'good work' - task discretion, job security, control over the pace of work, collective voice mechanisms, for example - do not appear to be among the favourite practices of PE people management.

"Also noticeable among PE firms is a hostility towards trade unions that is more pronounced than in the population of private sector managers as a whole. Some 40 per cent say they are openly hostile. Just one in ten managers has a positive attitude."

The report also says private equity outfits tend to be highly secretive. It says we need systems that will ensure we get better information and there's more accountability. That's particularly important because debt ratios among private equity firms are so high that they may be at risk from interest rate changes, or destabilising financial shocks.