Two whistleblowers on the US drone programme have joined campaigners in Brussels ahead of a European parliament hearing on the use of armed drones.

Former military technicians Cian Westmoreland and Lisa Ling both worked on the high-tech infrastructure on which the drones flying in Afghanistan rely. They have now come forward as critics of the US drone programme.

At an event this week, they spoke about strategic flaws in the drone programme and the risks of civilian casualties in drone warfare. On Thursday, they attended the parliamentary hearing where campaigners spoke of the impact of drones on civilian populations and the lack of compensation or recognition of their losses for the families of those killed and wounded.

Britain is currently the only European nation to use armed drones, but the European parliament believes this is on course to change, and has tabled a resolution calling on states to make sure that their drone operations are lawful and transparent.

Unmanned warfare is an especially thorny issue in Germany, where Ramstein US air force base is believed to serve as a key node in the US’s international drone infrastructure, including for controversial strikes taking place in countries where the US is not officially at war, such as Yemen.

Westmoreland told the Guardian he was driven to speak out after being given a performance award congratulating him because the signals relay station in Kandahar he had helped build had contributed to 2,400 missions and 200 “enemy kills”. This made him feel “horrible”, he said.

Adding to his queasiness, drone operators in Kandahar revelled in showing colleagues “drone porn” – footage of strikes – he said. “That never really sat well with me.”

“Doing something abstract like working on equipment and trying to work out what the overarching impact was has led me down a road to being more understanding of the global drone programme,” Westmoreland added.

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Although often portrayed as unmanned, drones are in fact “hypermanned”, he said, with thousands of people from different agencies and different countries feeding into a global network.

Some MEPs seemed to have a “total disconnect” from parts of the hearing, especially a video in which the brother of a cleric who had been killed in a drone strike described the impact on his family.

“One of them was playing on their cellphone while this was going on,” he said, although others were more receptive. “The connection needs to be made that if strategic and military goals are to be fulfilled, civilian lives must be respected.”

To Ling, the hearing seemed to be “the first stages of where the EU is going as a whole” on drones, she said. “I feel like they are exploring issues of what does participation in the drone war or extrajudicial killing actually look like.”

Ling said she had been amazed by “how little the public knew” about the US drone programme and its consequences. The narrative around drones had been “sanitised”, she said. “As citizens we need to have some conversation about the things that are in the dark … The people who are out of the picture are the people who are on the ground within the drone programme, and the victims.”

Ling’s work was on the drone programme’s distributed ground system, the global network through which data gathered by drones is collated and analysed. She was based in California, which she said led to a “schizophrenic existence between war and peace”. “The distance between what I was doing and the people who I knew was a huge chasm.”

She had become critical of the distant nature of warfare. “No matter how accurate your weapon is, if you’re not there, you’re not going to have full situational awareness,” she said, adding that for people in the remote and very poor areas that are the targets of many drone strikes, this advanced technology was “the only thing they see of us” and this created a “disconnect” with countries where drones were being deployed.

Ling was disturbed by the lack of certainty over who was being killed, comparing the treatment of refugees with that of suspected terrorists by the drone programme. “[We are stopping refugees coming into our country because we can’t identify them and keep our country safe. If we can’t identify them, how can we identify people we are killing with drones?” she asked.

She added: “Humanity has been taken out of the decision: there has been a lot of talk about the plane itself and how cool the technology is … but not a lot of conversation about the people who are affected.”