A Birmingham company which sells essays to university students has admitted helping students to cheat in an undercover BBC investigation.

The Edgbaston-based operation, called Elizabeth Hall Associates, provides a " ghostwriting" service to students to help them get a degree.

It was highlighted as one of the least ethical of a number of firms producing customwritten essays for between £130 to £200 in an investigation for BBC Radio 4.

Most of the companies claimed the essays were intended to be used as models to aid research.

But Elizabeth Hall told the BBC: "Technically we ask you to sign a declaration that it's a model. We expect you to customise it but I cannot see any reason why you cannot just hand it in."

Asked by the reporter whether she would be caught out, she said: "You won't have any problems with that, it's watertight."

Ms Hall charges £50-anhour for her services. When contacted by The Birmingham Post two years ago she boasted her work could not be detected by new anti- plagiarism software.

Another London- based company approached in the investigation admitted that what it was doing undermined the education system.

"I am using my brain so that they can sit in a bar," said a spokeswoman.

But Professor Charles Oppenheim of Loughborough University's Department of Information Science, who graded a sample of three customised essays, claimed students were being ripped off.

He found the best example would get a high 2:2 while the worst would receive a third.

The internet has fuelled a growing trend in students ripping off other people's work and passing it as their own.

They look up articles on the web that answer their set essay question, cut and paste paragraphs into their own copy and rewrite the material to avoid detection.