Parliament has been accused of operating a form of apartheid after a report found that minority ethnic staff were asked to show their security passes more often than white counterparts.

Black and minority ethnic staff who responded to a survey carried out last year also complained that historic parliamentary rules meant that they were not allowed to eat or drink in the same rooms or even use the same toilets as the mostly white members of the House of Lords.

Responding to the findings, Commons authorities acknowledged that the higher representation of BAME staff in lower pay bands meant they were less likely than their white colleagues to have access to certain areas. They have since opened up access to some facilities.

The research carried out by workplace equality network ParliREACH listed “examples of times when they felt that the lack of diversity and understanding of race had resulted in racist (inadvertent or otherwise) behaviours”.

These included senior managers “getting people’s names wrong or mixing them up with other BAME colleagues”; disparaging remarks such as being told “you sound just like” another non-white MP and Spanish speakers being warned “everyone here in parliament speaks English”.

All of those questioned “described themselves and other BAME colleagues being more frequently and more forcefully asked to have their passes checked”.

The study, titled Stand in My Shoes: Race and Culture in Parliament, recommended that the hierarchy of access to restaurants, toilets and other parts of the parliamentary estate – which prevents staff from using the same facilities as politicians – be removed. “These reinforce power relationships and lead to a disproportionate number of BAME staff being questioned when trying to use parliamentary facilities,” it said.

It comes after more than half of black, Asian and minority ethnic MPs said they had experienced racism, racial profiling and prejudice from their fellow MPs in a survey carried out by ITV News.

The parliamentary authorities said the serious issues disclosed in the ParliREACH study were “deeply worrying” and vowed to take action to tackle “ethnic institutional and structural inequality”.

They have now opened up access to the House of Lords’ exclusive riverside terrace where chairs were previously reserved for peers only, and removed old-fashioned signs that limited access to toilets to “peers and peeresses”.

Ed Ollard, the clerk of the parliaments – the most senior official in the House of Lords – said in written evidence to the home affairs select committee that the findings of the ParliREACH report were deeply worrying.

He admitted: “At the time the ParliREACH report was written, access to the House of Lords terrace was limited to staff above a certain grade.” Ollard said the Lords management board agreed to remove the restrictions on access to the terrace and “equalise access for staff to other catering facilities”.

And although he insisted there were “no restrictions on who can use the toilets in the House of Lords”, he admitted “some [misleading] historic signage suggesting use was restricted to ‘peers’ or ‘peeresses’ remained in place”. Nine signs are believed to have been removed.

John Benger, clerk of the house – the Commons’ main constitutional adviser – admitted in separate evidence to the committee that non-white staff had been disadvantaged by the system until now.

“There have historically been access restrictions in place across the estate, based on grade and seniority. As there is a higher representation of BAME staff in lower pay bands, this has meant that BAME employees have been less likely than their white colleagues to have access to certain areas.”

He said that work was under way to “tackle ethnic institutional and structural inequality in the house”.

Staff in the Commons now have to undergo training that includes “raising awareness of privilege” while those on recruitment boards have to take “unconscious bias” courses.

Imran Khan, QC, lawyer for the family of Stephen Lawrence, said the access restrictions were clear examples of institutional racism. He told the Guardian he was appalled when he first heard about them at the launch of the equality report.

“I had thought that such things happened either in apartheid South Africa or the deep south in the USA many years ago and here it was alive and well in the beating heart of our democracy,” he said.

“I know that there are critics of institutional racism and they should look at this as a clear example of how it works: no one in the Houses of Parliament deliberately set out to create a system where black people couldn’t use certain facilities but, because of the policies and procedures that existed, this was precisely the outcome.

“I am so pleased that this has now been changed but I am shocked that it even existed.”

A spokesperson for the Lords said: ‘‘The House of Lords administration is determined to ensure that all who work for the house are treated equally and with respect and creating an inclusive working environment.

“As part of this work, the board decided to remove access restrictions to catering facilities based on grade of staff, and remove misleading historic signage suggesting some toilets were restricted to members of the house.

“All signs have now been removed and replaced. This was part of our wider inclusion and diversity strategy.”

A House of Commons spokesperson said the institution had been undergoing a cultural transformation programme over the past year, and “the decision to change the access rules is a reflection of this ongoing move to create an environment where everyone can thrive”.

“By introducing more inclusive rules and eliminating distinctions based on staff grade, we will ensure all members of the parliamentary community are valued and respected,” they said.