For many years, it has been a crucial exam aid which has helped students plan just how much time they have got to write an essay or solve a mathematical puzzle.

But now students are to be banned from wearing watches in exams – for fear they might use them to cheat.

The Joint Council for Qualifications (JCQ), which oversees exam regulations across the country, had already brought in rules that no smartwatches, such as the Apple Watch or the Fibtbit Blaze, can be taken into examinations.

The move came around the same time as universities brought in the same rules, as smartwatches able to receive telephone calls and emails became increasingly popular.

But now assessors have changed the rules again so that students cannot wear even non-smartwatches on their wrists.

Instead they must take them off and put them on the desk in front of them.

'The risk is that anyone could be communicating within the exam,' explained Richard Cranmer, headteacher of Archbishop Sancroft High School (ASHS) in Harleston.

'There are some smartwatches that are difficult to on first glance differentiate one that is and one that isn't.'

Mr Cranmer said the benefit of the new rule is that invigilators can check watches in exam halls containing hundreds of young people quickly and easily, without having to put even more pressure on students.

'We want students to be entering the exam hall in the right frame of mind,' he said.

'We need them to be as least stressed as possible, and calm and focusing on the exam – not getting into a discussion on whether that's a smartwatch or it isn't.'

Most exam halls have clocks which students can use to help plan their time.

Invigilators will also flag up when they have just a few minutes left, but many students prefer to use digital rather than analogue clocks.

Those with poorer eyesight also prefer to have a watch in front of them which is clearer to see.

Mobile phones and MP3 players are also banned from exams, as are non see-through pencil cases.

The JCQ's information for candidates sitting written examinations states: 'Possession of unauthorised material is breaking the rules, even if you do not intend to use it, and you will be subject to penalty and possible disqualification.'