It is the responsibility of ministers to ensure existing security protocols are followed, Downing Street has said amid claims Robert Jenrick left his ministerial briefcase unattended on a train.

The Sun newspaper reported that witnesses had seen the immigration minister leave his red box unattended for at least four minutes last week.

A spokesman for the minister strongly denied any suggestion that the politician had abandoned the box.

Asked whether the Cabinet Office is investigating the matter, the Prime Minister’s press secretary refrained from commenting on the specifics, highlighting that they are yet to receive all the relevant details.

She told reporters in Westminster on Monday: “The PM believes that all ministers should follow the guidance set out around maintaining security and Government business.

“I don’t believe as of yet there is any update. It’s up to ministers to make sure that they follow the guidance.

“There’s a bit in the ministerial code about maintaining security of Government business and it’s up to ministers to make sure that they ensure that that happens.

“It’s a long-standing position that I don’t comment on security arrangements, but that guidance should be followed.”

On whether Downing Street had concerns there was a breach of the ministerial code, the press secretary said: “I don’t have all the details of what actually happened and I haven’t spoken to the PM about it.

“But he believes that all ministers should follow the guidance set out around maintaining the security of Government business.”

According to the report, Mr Jenrick was on a train back to his Newark constituency on Friday morning.

The paper also published pictures that it said shows the red box on a seat in a first class carriage on the train.

His spokesman said: “Mr Jenrick was working on the train throughout the journey, with his ministerial box close by at all times.

“He sat in the seat directly to the left of this misleading photo and he left the train with his locked ministerial box.”