Pair say they were detained for 27 hours after filming working conditions of labourers from balcony of hotel

Two German broadcasters have said they were detained by Qatari police this month as they attempted to investigate the plight of migrant labourers building infrastructure for the 2022 World Cup.

Peter Giesel, a film-maker and the head of a Munich-based production company, and his cameraman Robin Ahne were detained for 27 hours after filming the working conditions of labourers from the balcony of the Mercure Grand hotel in Doha.

The pair were following up on the Guardian's investigation into the conditions endured by many of the 1.2 million migrant workers who have flooded into the country to fuel a £100bn-plus construction boom before the football tournament.

"They said they just wanted to talk to us, but it wasn't clear about what," Giesel told the Guardian. "But the interrogations went on for several hours and then the security police got involved. They were talking about us sparking a riot by talking to the workers … and that's why we got detained and put in jail."

The pair, who say they were treated well while in custody, were told their equipment was being confiscated as they had been filming without permission.

"We went to the Nepalese embassy and it was flooded with workers trying to get their passports and documents back," Giesel said. "They tried to manipulate some of the footage and erase some. We weren't finished with the shooting in general, but afterwards I didn't have the nerve for it any more."

Documents obtained from the Nepalese embassy in Doha revealed last month that at least 44 Nepalese migrant labourers died between 4 June and 8 August, more than half from heart attacks, heart failure or workplace accidents.

International trade unions said up to 4,000 workers could die before a ball is kicked in 2022 if nothing was done to improve conditions for the workers, many of whom are heavily in debt and tied to their employers by law.

The Qatar 2022 supreme committee, which is overseeing preparations for the World Cup and has senior representatives from all the key government departments to ensure it is aligned with a parallel 2030 masterplan, has promised to take the issue of worker's rights seriously.

Before a key meeting of the Fifa executive committee in Zurich this month, the supreme committee chief executive, Hassan al-Thawadi, said the tournament would not be "built on the blood of innocents".

Fifa's president, Sepp Blatter, said he would visit the recently appointed emir to discuss the issue, but drew criticism from campaign groups for promising that the World Cup would go ahead regardless and claiming there was "plenty of time" to resolve any problems.

The International Trade Union Confederation called the Qatari response to an international outcry over the issue "weak and disappointing".

Giesel and Ahne were seized and held on 3 October, at exactly the same time as Fifa's executive committee was discussing the issue in Zurich.

The pair were released after friends and family got in touch with the German embassy in Qatar, prompting the German government's human rights commissioner to get involved.

Giesel said they had been treated well and even invited back to Qatar. "They were explaining, saying we know everything's not right in our country," he said. "But I think I should go back one day, just to make sure they didn't fool around with us too much and that what's been said in public there is in some way true. I can't say I will go back, but I might go back."

The footage shot by the German broadcasters has been acquired by Sky Sports News.

Last week an 18-strong delegation from the Building and Wood Workers' International union claimed they had been denied access to a construction site when they stopped as part of a surprise inspection visit.

The group was attempting to examine conditions on a construction site at Lusail, an area 44 miles north of Doha where an entire new city is being built including the stadium that will host the 2022 World Cup final.