Asif Ahmed, 28, describes how he was detained and asked to spy guardian.co.uk

People from ethnic minorities are up to 42 times more likely than white people to be the target of a counter-terrorism power which allows the stopping and searching of the innocent yet grants them fewer rights than suspected criminals, official figures seen by the Guardian show.

The power is contained in schedule 7 of the Terrorism Act 2000, which allows police to stop people at ports and airports for up to nine hours without the need for reasonable suspicion that they are involved in any crime.

The figures have led to accusations that police have resorted to "ethnic profiling", which they deny.

British Muslims have given written statements to the Guardian alleging that the police and the security service MI5 are abusing the power by holding people and pressing them into becoming spies.

Those stopped have no right to maintain their silence, and failure to answer questions can be a criminal offence.

Questioning can begin without a lawyer present and those stopped must pay for one themselves if they want legal representation.

The authorities fear the random nature of schedule 7 means a legal challenge could see the power struck down for being arbitrary, a counter-terrorism official said. This is what eventually happened to the part of the act that allowed stop and search in the street without any suspicion, which was ruled unlawful by human rights judges.

The uncovering of official figures by the Guardian is the first time an ethnic breakdown of who is stopped under schedule 7 has been made public.

The calculation that Asians are 42 times more likely than white people to be stopped under schedule 7 is based on comparing the percentage of Asians in the UK population to the percentage of those stopped under schedule 7. Ethnic breakdowns for those entering and exiting the UK are not available.

The disproportionality faced by ethnic minorities is at its most pronounced where a person is stopped and questioned for over an hour. White people make up 19% of stops, Asian people 41%, black people 10% and others (including Middle Eastern and Chinese) 30%.

Asians make up 5% of the UK population, black people 3% and others 1%. White people make up 91% of the population.

Where people are stopped and held for under an hour, the breakdown is: white people, 45% of stops; Asian people, 25%; black people, 8%; other ethnicities, 22%.

One of those stopped, Asif Ahmed, 28, said he was asked to spy after landing at Edinburgh airport.

He said he was separated from his wife and taken to a room and told he must answer questions about his beliefs and faith. "They asked if I would like to work with special branch, to keep an eye on the Muslim community in Edinburgh. They asked me three times. They said do it covertly."

Despite official claims that profiling on the basis of ethnicity is banned by the police, the official figures give strength to the argument that people are having their human rights infringed on the basis of what they look like and which god they pray to. Those stopped can also have their DNA taken and stored.

Ben Bowling, professor of criminology at King's College London, said the data undermines claims ethnic profiling is not being used. "They lend weight to the view that ethnic profiling is going on," he said. "The use of these powers at the border should be based on reasonable grounds and in ways that are properly transparent and accountable. At present they are opaque and unaccountable and seem little more than arbitrary and discriminatory, especially from the point of view of the person detained without reason."

One person subjected to a schedule 7 stop has provided a written statement alleging an MI5 officer tried to recruit him as a spy. When he refused, he says he was threatened with torture abroad.

Another, Alam Sheikh, 29, was stopped under the counter-terrorism power in January at Gatwick airport after a short holiday with friends in Morocco.

He was baffled when asked by police if he was involved in the Arab uprisings: "They asked do you know anyone who is part of the protests?

"One of my friends is a trainee lawyer. Even he was shaking. It wasn't fair. Most of us were smartly dressed. It wasn't like we were wearing Arab clothing or beards."

An exact figure on the disproportionate use of schedule 7 is difficult to arrive at because no figures are kept on the ethnicity of people entering and leaving the UK. Police forces have claimed releasing an ethnic breakdown of figures force by force could damage national security, and thus have previously refused to release them when requests were made under freedom of information legislation.

The figures published on Tuesday were released following a freedom of information request from the Federation of Student Islamic Societies.

In 2009 the National Policing Improvement Agency issued guidelines to officers about the use of the power, warning against ethnic profiling. "Examining officers must take particular care to ensure that the selection of people for examination is not based solely on their perceived ethnic background or religion," the agency said. "The powers must be exercised in a manner that does not discriminate ... to do so would be unlawful."

The guidelines make clear that ethnic profiling would damage the police: "Officers should be aware that the way in which people are selected has a potentially far-reaching effect on the public and their acceptance of counter-terrorism powers.

"Misuse of the powers can damage the relationship between the police and sections of the public."

But even some serving officers say the official selection criteria given to police makes it more likely officers will seek out those linked to Muslim communities. The guidelines talk of basing selection on "any information on the origins and location of terrorist groups" and "possible current, emerging and future terrorist activity".

Zaheer Ahmad, president of the National Association of Muslim Police said: "We are concerned about the disproportionality reflected in the number of people stopped from ethnic backgrounds – we have seen no acceptable reason as to why this is taking place. The police service must take an intelligence-based approach to minimise the impact of this power on the travelling public."

In 2009-10, 85,557 people were stopped and examined at UK borders under the schedule 7 powers. The government said: "A very low percentage of 220 million passengers travelling through UK ports were stopped, with only 0.03% of those travelling being examined."

John Donlon, the Association of Chief Police Officers' national co-ordinator for ports policing, said: "Schedule 7 of the Terrorism Act 2000 is important legislation in support of national security work at ports.

"The examining officers' code of practice enforces that the examination of a person cannot be based solely on perceived ethnicity or religion. Activity is intelligence-led and officers deployed at ports do not single out particular ethnic groups for examination."

• This article was amended on 24 May 2011. In the original, the ninth paragraph said that "42 times as many Asians are stopped as white people". This has been deleted and replaced with the summary given in the article's introduction.