A 35-year-old man has been arrested on suspicion of causing grievous bodily harm after a suspected acid attack outside a school in west London on Monday.

The incident outside Westminster Academy left a 14-year-old girl with “potentially life-changing” injuries, as well as injuring a 16-year-old boy and a member of staff who rushed to help.

The Metropolitan Police said the man was arrested on Thursday morning and remains in custody.

Officers on patrol were flagged down by school staff following the incident in Alfred Road, Westbourne Park, at shortly after 4.40pm on Monday.

The 14-year-old girl who sustained injuries which are “being treated as potentially life-changing” returned to hospital having been briefly discharged by doctors, police said.

The 16-year-old boy has been discharged from hospital, as police said his injuries were “not as severe as the girl’s”.

Detective Superintendent Scott Ware, investigating the incident, said on Thursday: “The investigation team has been working tirelessly to piece together the events in which two young victims, aged 16 and 14, were approached outside the school by a lone man who threw a substance at them before fleeing.

“We launched an urgent manhunt to identify and arrest the man responsible for this horrific attack. I am pleased to confirm a man was arrested in the early hours of this morning in connection with the incident.

“The 14-year-old girl sustained serious injuries and has returned to hospital having been briefly discharged by doctors.

“It may still be some time before we know the true extent of how serious her injuries are, but at this time they are being treated as potentially life-changing.

“The 16-year-old boy has now been discharged by the hospital and fortunately his injuries are not as severe as the girl’s.

“A member of staff from the school also sustained injuries as she rushed to the youngsters to provide first aid to them.

“We will maintain a visible policing presence outside the school and will continue to work closely with the school and local authority.”

Police urged anyone with information about the incident to call the investigations team on 020 7175 4652 or by contacting Crimestoppers on 0800 555 111 and quoting CAD 4987/30SEP.

Mr Ware added: “If you were in the vicinity of Alfred Road around the time of the attack and have dashcam footage that could prove key to our investigation, we ask that you urgently get in touch with us.”