A five-month investigation by Liberal Democrat chief whip Andrew Stunell has uncovered advice given to civil servants by Labour spin doctors on how best to answer parliamentary questions.

Cabinet office minister John Prescott should be provided with short sentences that are "punchy and easily spoken aloud" according to documents from his department.

The deputy prime minister is famed for his verbal mistakes, including referring to the G77 group, and mispronouncing "Milosevic".

Advice for Treasury mandarins reads: "It is legitimate to exploit the parliamentary process to obtain good publicity for the government's policies and record and to point to flaws in alternative policies."

Advice on written answers from the Department for Education and Skills states that answers "should enable the minister to be in charge of the issue, rather than on the defensive".

Said Stunell: "This is amazing. John Prescott is supposed to be second in command of the country.

"This guidance demonstrates a major difference between the standards the public are told to expect from government and the diet of half-truth and distortion that is delivered in parliamentary answers.

"I am particularly astonished to discover that special advisers are seeing questions before answers are drafted, they are amending them after they are drafted and then have responsibility for final clearance.

"Partisan briefing is required of civil servants as a matter of routine. It is obvious that many of these changes bear the prime minister's personal stamp."