A last-ditch attempt to evacuate all the British embassy guards on one of the final flights out of Afghanistan has failed, leaving them increasingly frightened about their future.

The international security company GardaWorld, which employed about 200 Afghan staff on contracts to protect the British embassy in Kabul, arranged 10 buses to collect their former employees to take them to the airport before dawn on Thursday.

A clear passage had been negotiated with the Taliban, allowing the buses to pass the checkpoints, and the convoy arrived safely but was not given permission to enter the airport gates.

The guards and their families remained in the buses outside the airport from 7am until about 6pm when explosions were heard on the other side of the airport perimeter, forcing the operation to be abandoned.

“We were very optimistic and hopeful that this was going to happen, and it hasn’t and these people will be devastated – rightly so,” said Oliver Westmacott, the president of GardaWorld’s Middle East operations.

The guards said it was a terrifying experience, particularly for the children. One woman went into labour on one of the buses during the long wait, and had to be taken off and transported to hospital.

Although US officials were cooperative and ready to allow the buses into the airport, clearance to enter does not seem to have been given by the British officials processing evacuation visas.

“Despite an assertion from government spokespeople at the end of last week that the British embassy security people were going to be given clearance to leave, it has subsequently become clear that there are an awful lot of people that they were trying to get out and the British embassy security people were not top of the list,” a source close to the evacuation attempt said. “It was a bandwidth capacity issue.”

After hearing the explosion the guards left the buses and fled home independently. “The Taliban were shooting in the air to make people get away from the airport. We had to run 500 metres and then find cars to take us back home,” one guard said.

They were devastated at the failure to get them out of the country in the final hours before the airport is closed to people trying to flee.

“At the last moment the UK government and GardaWorld really wanted to be heroes of this tragedy but unfortunately didn’t happen,” one of the guards said. “But they could have done it better with better management, days earlier, when there was no rush. Our life is full of tragedy now, we live in fear.”

There was now concern that their safety would have been further compromised by the evacuation attempt, because personal information had been shared with the Taliban in order to organise safe passage to the airport, he said. “Our normal life will now be much restricted; now that they have complete information about all of us.”

Several said the emergency evacuation attempt had been organised too late, weeks after they first tried to highlight their concerns that they were being abandoned by the UK government. Many applied for the UK’s emergency evacuation scheme, the Afghan relocations and assistance policy (Arap), when it was first announced in May, but were told in July they were not eligible because they were not direct embassy employees, but had been hired through the outsourced GardaWorld contract. Their contracts were terminated this week, days after the closure of the UK embassy.

After the guards’ predicament was highlighted in the media, the government made an unexpected U-turn last Friday and a spokesperson said: “We will help all those Afghan security guards contracted through GardaWorld to protect the embassy. They will be granted the right to enter the UK and we are now working through the challenging logistics of getting them out of Kabul.”

Initially GardaWorld hoped the Ministry of Defence would help with the evacuation operation, but when it became obvious this was not going to materialise the company made its own attempt to get its former employees out of Afghanistan, in a similar operation to one it mounted last week to evacuate all its expatriate staff. Sources said US officials had successfully worked with GardaWorld to facilitate the evacuation of guards who had performed similar roles at the US embassy in Kabul, and said the UK operation to remove people had been less well organised and not as well resourced.

Westmacott said the company would continue to try to help its former staff to leave. “Our message to our people is that the Arap process is ongoing, and our people need to be patient to wait for those approvals,” he said.

The Foreign Office has been contacted for comment.