It is understood a student working at law firm SJ Berwin worked until five in the morning after being asked to help a colleague on a document for an international arbitration. 

Graduate recruitment partner Nicola Bridge has since responded in a statement: "Vacation students are sometimes invited to take part in work such as deal competitions and trial preparation, which can run into the night, and we're keen to offer them the opportunity to observe and help with some of the more exciting parts of the job."

She admitted, however, that the firm should not go beyond inviting the student, and directly request the long hours. "On this occasion we got it wrong," she said. 

"Last week a student worked through the night on a document for a big international arbitration. She willingly stayed and worked with a female colleague and did a great job, but she was actually asked to do so and that shouldn't have happened. IN future we'l stick to our policy so this doesn't happen again."

Students working on summer vacation schemes are usually paid about £300 ($450) a week.