The incident happened at Haberdashers’ Knights Academy, on Monday, September 8, shortly after 3pm.
The academy said that two girls, both aged 13 and not pupils at the school, were stopped by staff.
They said the situation was dealt with “swiftly and calmly” and that students were safe at all times.
A spokesperson for the school said: “The safety and wellbeing of our students and staff is always our top priority.
“We are taking all possible steps to ensure our young people feel safe.
“With support from the police, we are confident that together, we can prevent further disruption and maintain the safe and welcoming environment that our students and staff deserve.”
The school later wrote to parents, explaining that teachers on duty at the gates acted “straight away”, making sure the situation was “contained”.
The letter reads: “As students were leaving, two girls who do not attend our school tried to come onto the site.
“Although the incident was dealt with swiftly, calmly, and effectively by staff, the police were called immediately.
“Please don’t be alarmed if you notice an increase in their presence around the area, as we have requested this as an extra precaution to provide added reassurance for our school community.
“I know how worrying this may feel, but please be reassured that staff are always on duty at the beginning and end of every school day, and we are increasing both our presence and our vigilance to make sure students continue to feel safe and supported.
“Your children’s safety will always be our top priority, and we remain fully committed to making our school a safe, and welcoming place for every student.”
The Metropolitan Police, who was called to the school at 3.10pm, said that officers were called to reports that “a woman had entered the premises without permission,” but that she had left before they arrived.
No further incidents were reported, and enquiries are ongoing.
The academy, however, has reiterated that the incident involved two 13-year-old girls, not an adult woman.
A spokesperson for the Metropolitan Police Service said: “Police were called to a school in Bromley at around 15:10hrs on Monday, 8 September to reports of concern for the welfare of students.
“It was reported that a woman had entered the premises without permission.
“Officers attended the scene, but she had already left the scene.
“No further incidents reported.
“The investigation continues.”
