Children should use Google and Yahoo to improve their essays, according to the official exams watchdog.

Ofqual said putting keywords into internet search engines was a “good starting point” when researching pieces of coursework and dissertations.

But guidance sent out to schoolchildren in England warns pupils to be extremely wary when using other websites such as Wikipedia.

The on-line encyclopaedia – created using contributions from readers – was not “authoritative or accurate” and in some cases “may be completely untrue”, said Ofqual.

Children can also be easily tripped up by copying passages from websites containing American phrases and spellings – a clear sign of plagiarism.

The comments were made in a series of documents sent to pupils, parents and teachers warning against cheating at school.