The BBC has been accused of showing a bias against the Conservative Party.

A report by the Centre for Policy Studies found that during the 2004 Labour and Conservative Party conferences, while the amount of airtime each party received on the Radio 4 Today programme was roughly the same, Labour Cabinet spokesmen were given 50 per cent more airtime than their Conservative counterparts. 

The authors also complained of "disparaging or ambiguous introductions" for Conservative shadow ministers which Labour ministers did not face.

In addition, Conservative spokesmen faced more interruptions during shorter interviews than their government counterparts. 

While Tony Blair was able to speak uninterrupted for 375 words, the report argues that the longest uninterrupted passage for his Conservative opposite number was 211 words. 

Similarly, the chancellor managed to speak 342 words without being interrupted, compared to 112 for his shadow, Oliver Letwin. 

The BBC's coverage of each party's economic policies was singled out for criticism. 

During a second period of studying Today - from 31 March when parliament was dissolved to 15 April when the first week of election campaigning came to an end - the airtime given to Labour to discuss the management of the economy came to 37 minutes 49 seconds, compared to 16 minutes 30 seconds for the Tories. 

Gordon Brown's main interview lasted for 11 minutes 15 seconds, compared to five minutes and 18 seconds with the shadow chancellor on the same day.

A statement from the corporation dismissed the criticism - suggesting the study had been selective.

"BBC News takes impartiality very seriously indeed and is always open to constructive criticism, but we are disappointed at the poor quality of a report on supposed BBC bias by the Centre for Policy Studies," it said.

"The report is pseudo-scientific in tone and its methodology highly flawed and distorted.

"The research, undertaken by Minotaur Media tracking, deals with the 'Today' programme only and not the broad range of BBC journalism.

"The authors had been extremely selective in choosing two brief periods of monitoring - apparently excluding evidence that contradicted their thesis; the report is also shot through with errors and is self-contradictory."