An airline "abandoned" a 24-year-old autistic man who was flying to Heathrow from Dublin, his mother has said.
Jane Atkinson said she was told by multiple Aer Lingus staff that her son George Stookes would be cared for before, during and after his flight.
But she said he was not helped at the terminal in Ireland, was ignored on the flight and left on arrival at Heathrow.
Aer Lingus told the BBC it was investigating the matter with its assistance provider at both airports.
A spokesperson for the airline said: ''When a customer requests special assistance, Aer Lingus notifies departure and arrival airports to arrange contracted assistance providers, which was the case in this instance.
"They are responsible for providing necessary support to our customers."
Mrs Atkinson, from Sway in the New Forest, Hampshire, said although her son was high-functioning, "there's still a huge vulnerability".
Mr Stooke's stepfather, Martin Atkinson, usually travels with him to and from Dublin but was unable to as his own flight had been cancelled.
His mother said she had been assured someone would stay with her son at all times and make sure he was put on the plane safely.
But she told the BBC: "He was taken through security at Dublin - then he was abandoned.
"George is very stoic and he managed to go into a sort of robotic mode so luckily on this occasion he managed to make the journey safely."
"But if a stranger had come up to him and asked him if he needed help, he would have just gone with them."
Heathrow has apologised and said it had been sent information about a number of passengers on the flight requiring assistance less than one hour before it landed.
"We will clarify with the airline how information is shared to ensure any passenger requiring assistance on arrival has their individual needs met," it added.
Dublin Airport said in a statement it was "committed to providing accessibility and assistance for passengers with reduced mobility".