DCI Dave Whellams, of the Metropolitan police, said it was a "serious, horrible offence which required a degree of planning and calculation".

Witnesses testified in court that Konye planned the attack over the course of two years. "She has prepared for this over a number of months, even years, all resulting from a trivial（insignificant）, insignificant argument that everybody has in their everyday lives," Whellams said.

"But Mary Konye has taken this so far that she has planned this, disguised herself and followed Naomi on that night. The result today will give Naomi only some comfort but she is never going to be away from the fact that she is scarred. Every time she looks in the mirror she is going to be reminded of the fact, but it will enable her to start to get some closure."

Whellams said the true reason behind the attack had not been established. "They can't tell me really what the argument is – it's fashion, it's boyfriends, it's everyday things ," he said.

Dressed in black, Konye remained calm as the jury of eight men and four women at returned their unanimous verdict after seven and a half hours of deliberations. The judge, David Radford, said she would face jail when he sentences her on 7 March.

"I should make clear that, in my judgment, this is a case that will in all likelihood need a substantial custodial sentence," he said.

CCTV footage obtained by police after the attack showed Konye in a niqab following Oni as she left work at the Westfield shopping centre in Stratford at 11.30pm. The victim lost her hair and eyelashes in the attack and required skin graft surgery to cover her burns.

The jury heard that the day after the attack Konye sent a text message to Oni in hospital saying: "OMG, I can't believe it."

It is thought she copied an attack on the model and TV presenter Katie Piper, who was badly scarred and blinded in one eye in 2008. Oni told the court that Konye was aware of the impact Piper's ordeal had had on her after watching a television documentary about it.

The pair, who had been friends since secondary school, fell out in April 2011 when Oni allegedly accused Konye of texting her boyfriend and called her an "ugly monster".

Baljit Ubhey, the chief crown prosecutor for London, described the attack as "extremely brutal". She praised Oni for her "courage and dignity" in giving evidence during the trial.

"The use of acid as a weapon is cruel and horrifying," she said. "It can have a devastating（devastate） effect on victims and can cause long-term pain and disfigurement as well as emotional and psychological harm."

Konye, of Canning Town, east London, had denied throwing or casting a corrosive fluid with intent to burn, maim, disfigure, disable or do grievous bodily harm.