The leaders of three Sydney colleges have apologised after signing a letter to the federal education minister asking to preserve religious schools’ rights to sack or expel gay teachers and students.

Last week, 34 Sydney Anglican schools wrote to the government warning of an undermining of their faith’s core values if the federal government overhauls anti-discrimination laws to protect gay teachers.

On Tuesday evening, the final of the three headmasters followed suit in apologising to staff and students for the hurt caused after signing the open letter, stating it was the most humiliating moment of his career.