An official investigation has been launched after two immigration service staff working with asylum-seekers were found to have links to the British National Party, The Independent has learnt.

One guard employed to look after asylum-seekers at a detention centre has been forced to resign after his name was found on a membership list of the BNP. Another man has been suspended while his employer investigates alleged links to the same far-right organisation.

Both cases raise serious concerns about racism within the immigration system, where membership of extreme political groups has long been suspected. Over the past two years The Independent has helped reveal nearly 300 allegations of brutality, including 38 claims of racism, made by asylum-seekers about private security and immigration staff. Some of the allegations included abusive and racist language, in which refugees fleeing persecution were referred to as "monkeys" or told to "go back to their own countries".

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The only two services where membership of the BNP can be grounds for dismissal are the police force and the Prison Service.

In the case of the immigration service, everyone working in immigration removal centres or in the guarding or removal of asylum-seekers must sign a declaration making clear that they are not members of the BNP, Combat 18 or the National Front. Those who are found to belong to any group that promotes racism will lose their accreditation to work in the immigration system.

Last night, the UK Border Agency said it "will not tolerate racist behaviour by individuals working in immigration removal centres. All allegations are investigated and the UKBA can revoke an individual's accreditation to work for the agency or have any contact with detainees."

It is understood that a security guard resigned after a list of BNP members was leaked to the media last year.

In the case of the suspended guard, the investigation is being conducted by the private contractor. During his suspension, the man will not be able to work with refugees or enter any immigration building.

BNP policy on immigration stipulates: "We will also clamp down on the flood of 'asylum-seekers', all of whom are either bogus or can find refuge much nearer their home countries."

Last month the Home Office received another report, this time from its own complaints watchdog, that raised serious concerns about the treatment of complaints of racism made by asylum-seekers, many of which had been miscategorised as "poor service" complaints. The report, written by the Home Office's Complaints Audit Committee (CAC), and seen by The Independent, said senior officials had "joined us in voicing concern that serious complaints such as allegations of assault aggravated by racism have been handled as service delivery complaints and as a consequence have not been properly managed".

The Labour MP Diane Abbott said last night: "If it is true that staff employed to work with asylum-seekers and immigrants are members of the BNP then it is yet another sign that the Home Office are allowing for the mistreatment of immigrants in this country. For years, campaign groups and my colleagues and I have been pointing out that hiring private contractors to work as immigration guards is a bad idea. It seems we will now have more proof of this. People who come to this country deserve to be treated with the same dignity and respect that is afforded to citizens."

A spokesperson for Medical Justice, which helped compile a dossier of nearly 300 complaints of alleged abuse, said: "We hear detainees complain about racism on an almost daily basis and it's virtually unheard of for a complaint to be upheld. The sheer volume of detainees complaining suggests among certain immigration guards there seems to be a canteen culture of racism which can flourish if left unchecked. Detainees feel dehumanised."

In its report, the CAC further warned: "Complaints of racism have caused us concern, as failures to report and investigate them fully may leave the UK Border Agency liable to prosecution under the Race Relations Act and to other anti-discrimination legislation... We have learnt of special problems in the detention estate, where complaints forms have a tick-box marked 'racism' and where officials believe that racism has been widely used as an inappropriate add-on to service delivery complaints, such as a detainee claiming that he had been served cold food because of his ethnic origin.

"We have reservations about the accuracy of this view in light of Sir William MacPherson's definition of a racist incident as 'any incident which is perceived to be racist by the victim or any other person'. As we do not routinely audit service delivery complaints, we cannot calculate the extent of alleged misuse of the term 'racist'."

The CAC said the Home Office should have supplied all misconduct complaints alleging racism. "We received only four complaints of racism from Colnbrook [detention centre, near Heathrow Airport] in 2007. This would appear to be a low number of potential complaints according to evidence collected by the HMIP [prison inspectorate] team, whose survey yielded the information that 18 per cent of detainees said they had been victimised by staff on the basis of their nationality and 15 per cent said they had been victimised on the basis of their ethnic or cultural origin."