The parliamentary watchdog should help crack down on bullying MPs by publishing the number of people who have quit their offices, a trade union has said.

The Independent Parliamentary Standards Authority (Ipsa) has been criticised for refusing requests to release data on staff turnover in MPs’ offices, with union officials saying a lack of transparency allows “endemic” bullying to continue.

Jenny Symmons, chairwoman of the branch of the GMB union that represents MPs’ staff, said: “More often than not, a high staff turnover is a warning signal of a toxic work environment.

“Our GMB branch in Parliament has found time and again that bullying is an endemic cultural issue in MPs’ offices. Staff are demeaned, isolated, expected to be contactable at all hours and given impossible workloads.

“Abuses of power fester behind closed doors, and any attempt to prevent transparency of that gets in the way of stopping it.”

Ipsa has so far resisted freedom of information requests from the PA news agency regarding staff turnover, releasing only the numbers of employees starting and leaving work in MPs’ offices but redacting the names of the MPs.

The body said providing the names of the MPs could enable the public to identify individual members of staff by “triangulation”, and thus breach data protection rules.

But the anonymised data showed some MPs had extremely high levels of turnover, with more than five people leaving their offices every year when most have only four or five employees in total.

Ms Symmons, whose union has called for an independent HR department in Parliament, added: “Our campaign to reform the employment structures for MPs’ staff continues.

“But, until that is achieved, we call on Ipsa to play their part in the efforts to radically change the working culture in Parliament – and come clean on the offices where change is most needed.”

Warrington North Labour MP Charlotte Nichols also called for more transparency from Ipsa, saying there are “sadly too many examples of incredibly poor practice”.

“Staff turnover can be an important early indicator of where there are problems, but you cannot ascertain this information from data in the public domain such as job vacancy listings, as MPs are not required to publicly advertise roles, which means the full extent of the issue can be obscured,” she said.

“Ipsa is the only body which can track and monitor this, and it is only right that this information is released so questions can be asked about why some MPs have such an incredibly high turnover and why they cannot retain staff.”

A spokesman for Ipsa said: “MPs are public figures and scrutiny of them and accountability to the electorate are fundamental elements of democracy. However, the employees of MPs are not public figures, and any public interest consideration is very different from that of their employers.

“Ipsa believes that disclosing the name of the employing MP brings a high risk of the indirect identification of current and former staff.

“Ipsa is committed to improving the working conditions and welfare of those who work for Members of Parliament and recognises the hugely valuable work that they do.”