A four-strong BBC crew had been invited by the prime minister’s office on an official tour designed to show off new accommodation for migrant labourers, but were arrested by the security services while trying to gather additional material. They were interrogated and jailed for two days, before being released without charge.

The BBC’s Middle East correspondent, Mark Lobel, was one of those detained, along with his cameraman, a driver and translator. Lobel said his interrogators never explained why he had been held but showed him surveillance photographs of his movements in Qatar. “They had actually photographed my every move since I arrived,” he said.

The visit was part of a public relations drive, partly overseen by London-based agency Portland, in the wake of an international outcry over the slave-like conditions for workers exposed by a Guardian investigation in September 2013.

Since December 2010, when Qatar won the right to stage the 2022 World Cup, its government has come under intense criticism for the poor conditions in which many of 1.4m migrants live and work.

The government defended the arrests and said the BBC crew were trespassing. A German film crew were detained last month while making a documentary, after being accused of not having a valid permit.

The BBC team were detained the week before last, but news of the incident only emerged on Monday. The journalists were later allowed to take part in the official tour of a migrant accommodation block but their equipment has not been returned.

“We are pleased that the BBC team has been released but we deplore the fact that they were detained in the first place. Their presence in Qatar was no secret and they were engaged in a perfectly proper piece of journalism,” said a BBC spokesperson.

“The Qatari authorities have made a series of conflicting allegations to justify the detention, all of which the team rejects. We are pressing the Qatari authorities for a full explanation and for the return of the confiscated equipment.”

Fifa, which has come under fire for failing to use the leverage of the World Cup to press for changes to labour laws, said: “Any instance relating to an apparent restriction of press freedom is of concern to Fifa and will be looked into with the seriousness it deserves.”

The Qatari government’s head of communications, Saif al-Thani, said the BBC crew were arrested after departing from an official tour. He said: “We gave the reporters free rein to interview whomever they chose and to roam unaccompanied in the labour villages.

“Perhaps anticipating that the government would not provide this sort of access, the BBC crew decided to do their own site visits and interviews in the days leading up to the planned tour. In doing so, they trespassed on private property, which is against the law in Qatar just as it is in most countries. Security forces were called and the BBC crew was detained.”

He said other media outlets were able to report freely from the same camp the following day.

The Guardian was not present on the media tour but toured the same labour camps later that week with the assistance of Portland and the Qatari authorities, as well as visiting other camps unaccompanied.

Qatari authorities insist they are committed to reform but human rights groups have been critical of the pace of change since the dire situation for many migrant workers, whose numbers are expected to swell to 2.5m within the next five years, was exposed by the Guardian and others.

Despite some new accommodation and a new law requiring wages to be paid electronically, there has been little progress towards reform of the kafala sponsorship system that ties workers to their employers.

Nor has the government made progress on cataloguing the number of deaths and injuries among migrant workers, many of whom arrive in the country already heavily in debt due to unscrupulous recruitment agents.

Florian Bauer, one of the four journalists from German broadcaster ARD detained last month after unsuccessfully attempting to acquire a shooting permit, said it took three and a half weeks for his team to have their equipment returned. “You do have a responsibility if you want to host these big sporting events to open yourself up to scrutiny,” he said.

Trade unions and pressure groups also stepped up pressure on World Cup sponsors and Fifa to do more to improve workers rights and conditions.

Sharan Burrow, the general secretary of the International Trade Union Confederation (ITUC), said: “We remind people constantly it’s a police state. We have seen journalists harassed, journalists who have told us their stories. It is extraordinary they have gone to these lengths. It’s the police state operating as it does without the PR company having knowledge of it.”

The ITUC has been particularly virulent in its criticism of Qatar’s labour laws and was part of a new drive launched on Monday to persuade Fifa sponsors, including Adidas, Coca-Cola and McDonalds, to put pressure on Qatar to change.

The initiative, co-ordinated by the chairman of sportswear brand Skins, Jaimie Fuller, was also backed by Tory MP Damian Collins. “You’ve seen the conditions the workers are living in. If McDonalds beef cattle lived in those conditions you wouldn’t buy their burgers so why should we expect the men building the facilities that will host the tournament they sponsor to be living in those conditions?” said Collins, who fronts an organisation called NewFifaNow.

“The same applies to the rest of the sponsors. It’s not acceptable to turn a blind eye. Fifa has blood on its hands, as do the sponsors, for as long as they continue to turn a blind eye to what is going on there.”