Alison Boulton digs beneath the city's dreaming spires

I’ve been invigilating this week, and it’s been emotional. There has been one inevitability so far. The sun has shone brightly throughout the examination, but at the moment of release, when all the students head like wildebeest for the door, its bright rays reliably disappears behind a cloud.

Although my fellow invigilators are seasoned, I am not. The unexpected happens, and takes me by surprise. One student is too hot. Another suffers from a wobbly desk. A third needs an eraser. A fourth can’t see the clock. A fifth – well, and sixth, seventh and eighth must go to the loo – and we’re only ten minutes in. I feel foolish accompanying a six feet four rugby player to the lavatory, and waiting outside for what seems like an age, looking at notice boards on how to tackle stress, late nights in Oxford and having your bag stolen.

Some candidates ignore the communal start, preferring to keep their own time. They lope in ten minutes late and sit down at their desk, and stretch. Then they cast a casual eye over their examination paper, and wearily lift a pen. Next they stare at the top sheet for a while, and slowly, unwillingly, fill in their name. Then, they leaf through the pages, pulling faces of disdain or disbelief. Then they look out at the sunshine. Then, after an hour, they put up their hand – and leave. It’s all within the rules, and they know it.

Others sit down, place their pens and pencils carefully in front of them, eye the top sheet purposely and fill in their name. I warn them that any mobile phone found in the examination room will be deemed tantamount to cheating and may disqualify its owner. I read out a housekeeping list of what they may and may not keep on their desks. Most items share the common characteristic of transparency – including plastic bottles,of water which must have their labels removed. Even glasses cases must be open.

When I give the signal to begin, as the red second hand reaches the stroke of 12, the students turn over their sheets in perfect choreography. Then it’s heads down, and the only sound is the occasional sigh. Perhaps a student looks up for inspiration, or rechecks the finishing time, projected on a large screen at the front of the examination hall.

The tension is palpable. It gets to invigilators too. Countdown to the impending end is nerve-racking for all. When it comes to the ten minute warning, it’s as though another ripple of stress breaks out. It washes between the candidates and their carefully separated desks – isolated yet communal, they all feel it.

Although the start is uniform, the close of an exam is anything but. There is huge variation. A combination of subject papers are frequently sat at one time, each of diverse length. It is not just subject matter which varies. Students sitting the same paper have a range of finishing times. Candidates with specific learning difficulties may have up to 25 per cent extra time – all of which has to be calculated and put on the chart at the front of the room, colour banded to denote each candidate’s status. Others for whom English is a second language – and may need to consult a dictionary – also have an extra time allowance.

One thing’s for certain: when the scripts are collected and the candidates make for the door, we’re all relieved to have got the ordeal over and done with – even vicariously.