Strictly Orthodox school in London has issued an early warning to parents that pupils who let off smoke bombs or trigger fire alarms as part of high jinks for Purim can expect to be sanctioned.

Pupils involved in behaviour considered unacceptable last year will receive warnings and “refundable deposits” taken, Menorah Grammar, an independent boys’ school in Edgware, said.

Purim, the closest a Jewish festival gets to carnival, does not fall until late in March this year.

One source familiar with the school said, “This year they have decided to let everyone know well in advance that they will come down hard like a ton of bricks.”

Writing to parents this week, the school’s principal, Rabbi Yoel Rabinowitz said that over the past 18 months a clear improvement in behaviour among the vast majority of pupils had played “a major part in the school’s recovery”.

(Although the school is still officially rated as inadequate by Ofsted, a recent visit noted that leaders were dealing effectively with challenging behaviour from a small number of pupils).

Rabbi Rabinowitz said, “Unfortunately, last year, a small number of boys demonstrated unacceptable behaviour around Adar time [the month in which Purim falls]. This caused disruption across the school and impacted behaviour of others.”

Some of this, he added, was “not only disruptive but also, potentially, dangerous,” which brought brought the school “into disrepute”.

Triggering a fire alarm, letting off a smoke bomb or “riotous behaviour would not be tolerated and could lead to sanctions ranging from fines, withdrawal from entry to exams or exclusion.

Anyone who gives cover to perpetrators could also face sanctions, the school warned.