The BBC needs to take more care to ensure it is impartial, according to a report commissioned by the corporation.
The BBC has issued new guidelines on impartiality following the report
It accused the BBC of breaking its own guidelines by screening an episode of The Vicar of Dibley which promoted the Make Poverty History campaign.
The report also quoted former political editor Andrew Marr, who said the BBC has an "innate liberal bias".
However, it added that the BBC is "generally seen as impartial" and set out new guidelines for avoiding bias.
Twelve guiding principles have been introduced, which will complement the BBC's existing editorial guidelines.
The corporation says they are needed because of social and technological changes which have led to a spread of opinion beyond the traditional "left-right" political divide.
Among them is the statement that impartiality is "not necessarily to be found on the centre ground".
Other principles warn that impartiality should not lead to "political correctness" or "insipid programmes" and there must be room for controversial and passionate contributors.
The report said a seminar held by the BBC last year saw an element of support for the idea that "some sort of liberal consensus" existed in the organisation.
It notes that news programmes missed several emerging stories on Europe and immigration which it described as "off limits in terms of a liberal-minded comfort zone".
But "the report does not say that the BBC is institutionally biased," deputy director general Mark Byford told BBC News 24.
Drama, comedy, music and children's programmes are also expected to pay attention to impartiality, the document says.
It uses the introduction of the BBC's 3D weather maps in 2005 as an example of how the corporation can be seen as biased towards the south-east of England.
The Vicar of Dibley featured shots of an anti-poverty website
Because of the way the maps were tilted, they appeared to suggest that northern Scotland was on the periphery.
Although the problem was quickly ironed out, the report warned that "the continuing practice of giving temperature forecasts for conurbations rather than rural areas may suggest a presumption that the bulk of the audience lives in large cities, whereas the opposite is in fact the case".
The BBC's coverage of Live 8 and the Make Poverty History campaign was also singled out for criticism.
An episode of BBC One comedy series The Vicar of Dibley, written by Make Poverty History campaigner Richard Curtis, was commissioned without reference to the editorial guidelines, it said.
The London Olympics will be a "serious test," the report says
The sitcom showed Dawn French's character urging parishioners to support the anti-poverty campaign and may have breached the BBC's code, which prevents dramas from endorsing charities.
The report went on to warn that the London Olympics will provide a similar test of the BBC's impartiality.
"Coverage of international championships has sometimes drawn criticism that the British media are too preoccupied with British competitors," it said.
"That pull will be all the greater when the Olympic flame reaches British soil in what is likely to be the year of the Queen's diamond jubilee".
In compiling the report, the BBC commissioned a survey into its audience's views on impartiality.
Sixty-one per cent of people questioned said broadcasters may think they give a fair and informed view but a lot of the time they do not.
A further 83% agreed that broadcasters should report on all views and opinions, however unpopular or extreme some of them may be.
"BBC audiences believe that impartiality should not lead to political correctness," said Richard Tait, the BBC Trust member in charge of the report.
"The BBC agrees and one of our new principles makes clear that impartiality is no excuse for insipid programme-making."
Mr Byford, who was part of the report's steering group, said the findings were of great importance.
"Safeguarding impartiality is a big and challenging topic and the publication of the report should be the catalyst to a wide conversation and debate across the BBC."
The report was approved by the BBC Trust and BBC Executive Board.
The trust represents licence fee payers and ensures the BBC provides value for money, while the board is responsible for delivering the BBC's services in line with the priorities set by the trust.