Five years ago England’s exam system was described by its chief regulator as a “cottage industry”.

That phrase seems wildly inappropriate when you are standing in a hall the size of a football pitch filled with thousands of scripts moving around on conveyor belts.

“Industrial” seems the only term to describe what is going on, as completed answer books trundle to scanners, from where they will be sent electronically to examiners.

This is Hellaby, run by the exam board Edexcel. It is the largest exam paper processing centre of its kind in the UK and probably Europe. Some five million GCSE and A-level scripts will have passed through this warehouse-cum-factory by the time the exams season finishes next week. If your pupils take Edexcel’s exams, their scripts will have been here.

The centre, on the outskirts of Rotherham in south Yorkshire, handles 1.3 million sheets of paper a day during its peak period, from mid-May to the end of June. It is, perhaps, the embodiment of England’s staggeringly complex marking system. This summer, more than 90 per cent of its GCSE and A-level answers are being sent here to be scanned electronically.

Edexcel has been leading the way in the mechanisation of exams for the past five years, replacing examiners sitting at their kitchen tables marking a pile of scripts by hand with onscreen marking.

But its introduction has been controversial. The board, taken over in 2003 by the publishing company Pearson, which looks to make a profit, sometimes stands accused by markers and schools of being too hasty in its push to modernise marking - an allegation the company strenuously denies.

The level of security inside Hellaby is understandably high. Mobile phones are banned from the hall, to preserve the confidentiality of pupils’ answers. This also stops anyone photographing the contents of future exam papers, which are sometimes handled here.

Schools and colleges send scripts by Parcelforce. They are sorted into separate batches for each paper, then lifted in large crates by forklift trucks and stacked to the ceiling ready for processing.

The whole system is computerised, with each package of papers and each individual script bar coded so that it can be tracked at all times. Even the forklift drivers follow computerised instructions.

The scripts are then loaded onto a conveyor belt where shift workers screen out and store any notes or extra material a teacher might have included, such as a note saying a pupil was not well.

And scripts which cannot be examined on screen - for example, if the pupil has used extra sheets of paper, or has written in the wrong colour ink - are filtered out so that they can be marked in the traditional manner.

The scripts are then broken up into separate pages mechanically then scanned on one of 26 machines, with questions split up electronically and sent to examiners.

Dave Hansell, Edexcel’s head of operations, stresses the thoroughness with which the system keeps a track on all pupils’ papers. It is unheard of for a script to be lost.

Despite the numbers involved, Hellaby does not operate at full capacity. Those staffing it work in two shifts between 6am and 10pm, but not at weekends.

When Edexcel won the contract to mark national tests from 2005, Mr Hansell said it was envisaged that they would be scanned here too, and marked onscreen from 2006, which would have meant a total of 10 million scripts annually passing through the plant. But he said: “The Government was uncomfortable about moving towards that technology at that time.”

Edexcel lost the test marking contract to the US firm ETS, which has encountered problems after introducing technology on a much more limited scale this summer.

The Qualifications and Curriculum Authority remains enthusiastic about onscreen marking. England’s two other boards are proceeding more slowly. But there is little doubt Hellaby is the future.