Claims that asylum seekers are mistreated, tricked and humiliated by staff working for the UK Border Agency are to be investigated in parliament.

The home affairs select committee chairman, Keith Vaz, has called for an investigation following allegations that officials at one of the government's major centres for processing asylum seekers' claims express fiercely anti-immigration views and take pride in refusing applications.

Louise Perrett, who worked as a case owner at the Border Agency office in Cardiff for three and a half months last summer, claims staff kept a stuffed gorilla, a "grant monkey", which was placed as a badge of shame on the desk of any officer who approved an asylum application.

Perrett, 29, also alleges that one official boasted to her that he tested the claims of boys from African countries who said they had been forcibly conscripted as child soldiers by making them lie down on the floor and demonstrate how they shot at people in the bush. One method used to determine the authenticity of an asylum seeker claiming to be from North Korea was to ask whether the person ate chop suey.

Perrett, whose claims will become the basis for parliamentary questions from Jenny Willott, the Liberal Democrat shadow chancellor of the Duchy of Lancaster and Cardiff Central MP, said interviews were conducted without lawyers, independent witnesses or tape recorders. If a case was difficult, Perrett claims, she was simply advised to refuse it and "let a tribunal sort it out". Only cases raised by MPs appeared to be dealt with properly.

Perrett said she was given the power to make legally binding decisions on whether asylum seekers were granted or refused asylum after just five weeks' training. She also had the power to detain individuals and families for up to 28 days. Like her colleagues, she was obliged to sign the Official Secrets Act. She took legal advice before deciding to speak out publicly.

She claims the tone was set on the first day when one manager said of the asylum-seeker clients: "If it was up to me I'd take them all outside and shoot them." Another told her this was to be expected, adding: "No one in this office is very PC. In fact everyone is the exact opposite."

She told the Guardian: "I witnessed general hostility, rudeness and indifference towards clients. It was completely horrific. I highlighted my concerns to senior managers but I was just laughed at. I decided to speak out because nobody else was saying anything and major changes are needed at senior management level."

One of her cases involved a Congolese woman who had the right to remain in the UK. Perrett says a superior nevertheless decided the woman and her children should be removed, and asked officials whether there were any grounds to remove them. Frustrated, she approached a member of the legal department. His reply, according to Perrett, was: "Umbongo, umbongo, they kill them in the Congo."

Vaz said: "I am deeply concerned by a number of ex-UKBA workers who have spoken out about flaws in the points-based system and behaviour such as this. I will be writing to the chief executive, Lin Homer, to discover what steps are being taken to remedy this culture of disbelief and discrimination."

Willott said she was tabling a series of parliamentary questions. "Some of the cases which seem obvious to me are refused. UKBA has a responsibility to treat people as human beings, but from Louise's experience it seems that this does not always happen."

Matthew Coats, head of immigration at the UK Border Agency, disputed Perrett's claim that she raised concerns and the department declined to respond to her specific allegations. But he said the agency "expects the highest levels of integrity and behaviour from all our staff," adding: "We take all allegations of inappropriate behaviour extremely seriously."