British Airways flight attendants on board an Airbus A380 “superjumbo” vomited, became “spaced out” and had to use emergency oxygen after suspected “toxic fumes” were detected in the cabin during a long-haul flight, a leaked internal report reveals.

At least one crew member became so ill that he curled up on the floor and put a blanket over his head. Others displayed bizarre behaviour including “stuffing” food into their mouths while using oxygen masks and wandering around “lost” in the cabin.

The report, which has been seen by The Sunday Times, was written by the cabin service director (CSD), the most senior grade of flight attendant, who was in charge of the 22-strong cabin crew on a BA flight from San Francisco to London on October 25.

About 40 minutes after take-off, while the airliner was over Canada, crew detected a strong noxious smell similar to burning plastic and the flight was diverted to Vancouver. The captain declared an emergency, telling air traffic control that the problem was “toxic gas-type fumes”. After the aircraft landed safely, all the flight attendants and the three pilots were taken to hospital.

BA later described the incident as an “odour event”, prompting claims by the Unite union that it was downplaying the health risks of potentially toxic fumes in aircraft cabins.

The cabin air in most passenger jets is supplied from the compression section of the engine in a process known as “bleed air”. If seals inside the engine leak, it is believed that heated oil fumes can enter the air supply, contaminating it with chemicals that some experts believe can cause serious health problems.

The leaked report graphically describes the severity of the incident. It details how 12 crew members displayed symptoms that gave “cause for concern” and that eight of the nine crew members on the upper deck plus the captain used emergency oxygen.

After the smell was detected by a door towards the back of the main cabin and on the upper deck, the report says “it soon became apparent that more crew were behaving in a non-normal manner . . . [with] reports of dizziness, light heads, headaches, nausea, itchy red eyes, metallic taste in mouth, floating-type feelings, flushed, aggression and, most worryingly, forgetfulness and confusion, inability to think straight and converse in normal manner.”

It describes how one crew member said something “completely out of context” and seconds later had forgotten that he had said it. Senior flight attendants would “lose” colleagues who would say they were going to the lavatory but then ended up at the other end of the aircraft “not knowing how they got there”, it adds.

The CSD described “crew in corners on [the] floor with blankets over their heads” and “crew ‘stuffing food’ in their mouths while on oxygen”.

Crew members continued to complain of feeling ill after they left hospital, according to the report. One collapsed vomiting at Heathrow’s terminal 5 when they returned to the UK.

This weekend another flight attendant told how crew members were “sobbing” during a debriefing session at Heathrow and claimed that some staff are still off work.

“I can’t say how I would have acted in an emergency situation if I had to go through my drills,” said the source, who asked to remain anonymous.

Ciara Parkes, a showbusiness publicist who has represented the actors Jude Law and Ewan McGregor, was on the plane with her husband, Gus. She said they feared they were being hijacked because the crew were so panicked.

“I think that’s probably the most terrified I’ve been in my life,” she said.

She said her chest became “incredibly tight” and she struggled to stand during the incident. She claimed some passengers had bloodshot eyes. Four days later Parkes had a blood test that showed elevated levels of enzymes, which can indicate liver problems. She has had regular headaches since.

BA said its engineers had inspected the aircraft in Vancouver and “no fault was found”.

It added: “The safety of our customers and crew is always our top priority. We have shared our detailed and thorough investigation with the Civil Aviation Authority and fully comply with all safety regulations.”

Airbus said its aircraft are designed to “provide the highest level of cabin air quality”.