Dr Chris Willmott of Leicester university devised a plan four years ago to prevent plagiarism in academic coursework. Since then he has only had two cases.

He believes teachers can learn to recognise the writing style of their students so that they can see when submitted work deviates from that norm.

And if they suspect the work is not the student’s own they only need to type five or six words from the pupil’s essay on to a web search engine to check it.

“The fact that so many people have been visiting cheat sites is depressing, but not altogether surprising,” he said.

“It reinforces the need for all educators to ensure that our students can distinguish between appropriate and inappropriate uses of source materials.

“We need to be putting at least as much effort into plagiarism prevention as we are into plagiarism detection.”

Other signs, which show work has been lifted directly from the internet, include American spellings, changes to font or formatting for no reason, number references when there is no relevant reference at the end of the essay and references from obscure or mainly overseas publications.

Some students can be quite brazen about their cheating.

Dr Willmott said one colleague in his biochemistry department a few years ago was very impressed with one student’s essay.

He said: “In fact he thought it was extremely well-written and then he recognised it was from his own textbook.”

Dr Willmott and his colleagues have now taken preventative measures to stop it happening again.

Each year students are asked to do an exercise where they are given a short piece of text and seven versions of it and asked which are the plagiarised versions.

He says teachers can make life harder for cheats by specifying books or websites to be used for research and having an up-to-date knowledge of material in cheat websites. Dr Willmott also suggests teachers should ask pupils to make an oral presentation before submitting their work.