A Tunisian people smuggler has been jailed for 18 years for causing the worst boat disaster in the Mediterranean since the Second World War.

Mohammed Ali Malek was at the helm of an overcrowded vessel carrying up to 800 refugees that went down between Libya and Italy in April 2015. Judges in Sicily sentenced him to 18 years in prison on Tuesday for manslaughter, human trafficking and causing the disaster, fining him €9m (£7.5m).

Mahmoud Bikhit, a 26-year-old Syrian man accused of being his first mate, was handed a five-year sentence by judges in Catania for “facilitating illegal immigration” and a €9m (£7.5m) fine.

The pair were found to have commandeered a former fishing trawler crammed with desperate migrants, dangerously overloading the vessel before accidentally ramming it into a Portuguese container ship attempting to rescue those on board and causing it to capsize.

Mohammed Ali Malek (L) and Mahmud Bikhit who have been arrested on suspicion of being respectively captain and crew member of the migrant ship that capsized off the Libyan coast (EPA)

Malek and Bikhit were among only 28 people who survived the disaster that killed at least 700 refugees, including many who had been locked in the boat’s hold.

“While getting onto the boat I heard the smugglers say that they were going to try to get 1,200 on to the boat and that’s why they beat us to get us onto the boat,” said Said, a 16-year-old survivor from Somalia.

“But they stopped at 800 because it was full – we couldn’t even move. There was no food or water, the people that were put below were locked underneath.”

The boat got into trouble within hours of departing from the port city of Zuwarah, near Tripoli, on 18 April and started taking on water as passengers started to panic, with some attempting to escape to the deck and those on deck trying to find safety below.

Once in international waters, it sent out a distress call and Italian commanders dispatched the Portugese King Jacob container ship to help.

Its crew attempted to steer the ship to avoid collision and switched off its engines, but its captain said the refugee boat suddenly increased speed and smashed into its port side. The trawler swiftly lost balance and overturned. In less than five minutes it sunk.

Malek claimed he was “neither a criminal nor a murderer” in a letter to the BBC, claiming an unidentified African man had been steering the boat and blaming the King Jacob for causing the collision and sinking.

But officials in Sicily put the capsizing down to Malek’s steering of the trawler into the cargo ship and the panicked movement of passengers after the crash.

Speaking last year, Catania prosecutor Giovanni Salvi stressed that none of the Portugese crew were under investigation and that their attempts to help the ship in distress “in no way contributed to the deadly event”.

In pictures: Migrant boat disaster Show all 10 1 /10 In pictures: Migrant boat disaster In pictures: Migrant boat disaster Migrant boat disaster Rescuers help children to disembark in the Sicilian harbor of Pozzallo, Italy In pictures: Migrant boat disaster Migrant boat disaster A child is carried by a rescue worker as he arrives with migrants on the boat at the Sicilian harbor of Pozzallo In pictures: Migrant boat disaster Migrant boat disaster A migrant is helped disembark in the Sicilian harbor of Pozzallo, Italy In pictures: Migrant boat disaster Migrant boat disaster A boat transporting migrants arrives in the port of Messina after a rescue operation at sea Getty In pictures: Migrant boat disaster Migrant boat disaster Italian Coast Guard officers disembark the body of a dead migrant off the ship Bruno Gregoretti, in Valletta's Grand Harbour In pictures: Migrant boat disaster Migrant boat disaster Armed Forces of Malta personnel in protective clothing carry the body of a dead immigrant off Italian coastguard ship Bruno Gregoretti as surviving migrants watch in Senglea, in Valletta's Grand Harbour In pictures: Migrant boat disaster Migrant boat disaster Rescued migrants talk to a member of the Malta Order after a fishing boat carrying migrants capsized off the Libyan coast, is brought ashore along with 23 others retreived by the Italian Coast Guard vessel Bruno Gregoretti at Boiler Wharf, Senglea in Malta In pictures: Migrant boat disaster Migrant boat disaster Bodies of dead immigrants lie on the deck of the Italian coastguard ship Bruno Gregoretti in Senglea, in Valletta's Grand Harbour In pictures: Migrant boat disaster Migrant boat disaster Italian coastguard personnel in protective clothing carry the body of a dead immigrant off their ship Bruno Gregoretti in Senglea, in Valletta's Grand Harbour In pictures: Migrant boat disaster Migrant boat disaster Italian coastguard personnel in protective clothing stand on the deck of their ship 'Bruno Gregoretti', carrying dead immigrants on board, as it arrives in Senglea, in Valletta's Grand, Harbour

A 32-year-old Bangladeshi man, the first survivor to arrive in Sicily, said: “I and the others managed to survive because we were outside, but many of the others remained prisoners in the hold of the boat because the traffickers had locked them in and they finished at the bottom of the sea.”

Volunteers who joined the recovery effort described finding children’s bodies, shoes, life jackets and backpacks floating in the water.

It was the second disaster that week in the Central Mediterranean, following another sinking where more than 400 migrants drowned.

The successive tragedies drove calls for Europe to provide refugees from across the Middle East and Africa with safe passage to the continent but early rescue efforts have largely morphed into missions targeting smugglers, with humanitarian rescues a secondary objective.

Shortly after the April disasters, the main refugee route switched to the comparatively shorter and safer crossing over the Aegean Sea from Turkey to Greece.

But attempts by authorities to close the passage with the controversial EU-Turkey deal have made the treacherous Central Mediterranean crossing, now the deadliest in the world, the dominant passage for those fleeing war and persecution.