A report into the drowning of at least 27 people in a doomed small-boat crossing of the Channel has revealed the full story of the tragedy for the first time.

An independent inquiry is due to be held into the mass drowning, which happened after 33 people crowded into an inflatable craft which was launched from a beach on the French coast on the evening of November 23, 2021, bound for Kent.

After around four hours on the freezing waters of the Dover Strait, the vessel began taking on water. Realising the grave danger they faced, individuals packed into the craft – wholly unsuited to the conditions it faced – began raising the alarm via mobile phones.

A search and rescue effort was hampered by poor visibility and the lack of dedicated aerial surveillance, and the people on board the overwhelmed inflatable were ill-equipped and untrained for such a perilous voyage.

At least 27 people – including a pregnant woman and three children – are confirmed to have died after entering the water when their stricken boat sank. There were two survivors and four people remain missing.

Transport Secretary Mark Harper has announced an independent, non-statutory inquiry will be held to investigate the circumstances of the deaths.

The announcement follows the publication of a comprehensive Marine Accident Investigation Branch (MAIB) report into the tragedy, which revealed the detailed events of the sinking, and the emergency response to it, for the first time.

The report confirmed that on the night of the disaster there were multiple small boats attempting the crossing of the Dover Strait from France to the Kent coast. With each boat making multiple calls indicating distress it was “extremely challenging” for the coastguard to locate and identify individual vessels.

Investigators from the MAIB found that, because of the lack of surveillance available, coastguard operators were reliant on “limited information passed to them by French authorities” and mobile phone calls from the occupants of the boats as they tried to establish the exact nature of the unfolding tragedy.

As a result, the report recommends that officials at both the Maritime and Coastguard Agency (MCA) and Border Force develop procedures to ensure effective surveillance is possible when aviation assets are unavailable to monitor traffic in the Channel.

The MCA has also been instructed to work with the French authorities to improve the transfer of information between the UK and French Coastguard agencies “pertaining to migrant boats during crossing events”.

It is understood that the small boat carrying those who perished, including women and children, set sail from a beach near Dunkirk in northern France at around 9pm on the night before the alarm was raised.

Like the vast majority of the small boats used by people attempting to reach the Kent coast, it was entirely unsuited to the conditions it would encounter in the waters of the Channel.

The report states that the crossing “had been arranged by a network of facilitators in France” who had provided the boat and equipment that was used in the attempt to reach the British shore.

Heading west towards Kent, the vessel is understood to have become damaged and began taking on water at around 1am on November 24. Initially the occupants were able to keep the craft afloat by bailing out, but these efforts were overwhelmed and the boat’s inflatable hull began losing pressure.

Those on board made a last desperate attempt to re-inflate the boat using hand-operated air pumps they had been provided with, but they did not succeed. The alarm was then raised via WhatsApp communication to authorities on both sides of the Channel.

In one distressing passage, the report details frantic calls to the authorities as those on board the craft tried to summon help.

During these desperate appeals for help, screaming and shouting could be heard in the background, and one caller is said to have requested a helicopter before simply stating: “I am finished.”

The report states: “Some of the victims managed to cling to the submerged remnants of the boat; others drifted away. Over a period of hours occupants of the boat perished, with around eight reported to be still alive at sunrise.”

In determining the likely fate of those on board the doomed craft, the report concludes: “It is likely that many of the victims of this accident wearing flotation devices succumbed to the effects of hypothermia; however, any without flotation support would have succumbed over time to a mixture of cold water shock, cold incapacitation or hypothermia.

“Given the uncertainty over individuals’ survival time in cold water, and the range of time over which their deaths likely occurred, it cannot be determined whether individual victims died in UK or French waters.”

Commenting on the publication of the report, Andrew Moll, chief inspector of marine accidents said: “The events were complex with multiple inflatable boats that were unsuitable and ill-equipped for the journey attempting to cross the Dover Strait to England.

“The occupants were not trained mariners and their only means of calling for help was by mobile phone.

“Many boats made multiple distress calls and without dedicated aerial surveillance over the Strait it was extremely challenging for the coastguard to understand how many boats were attempting the crossing, their locations and their actual levels of distress.

“In November 2021, the UK’s response to the migrant crisis was still evolving and although the need for enhancements had been identified remedial action was still in hand.

“The report acknowledges that significant changes have been made since the accident. However, the Maritime and Coastguard Agency and Border Force are recommended to develop procedures to ensure effective surveillance of the Dover Strait is possible when aviation assets are unavailable.

“A recommendation is also made to the Maritime and Coastguard Agency to work with French authorities to improve the transfer of information between UK and French Coastguard agencies during migrant crossing events.”

Transport Secretary Mark Harper said: “I am grateful to the Marine Accident Investigation Branch for their report examining this tragic incident, and the government will carefully consider its findings and recommendations.

“As the report recognises, the operational picture in the Channel has changed significantly since 24 November 2021, and I know that HM Coastguard continuously seeks to learn lessons and improve.

“The inquiry I have announced today will allow a thorough and independent investigation into the circumstances of the deaths to take place, further to the MAIB’s report, to give the families of the victims the clarity they deserve. I know that the Coastguard will engage fully and openly with it.”