Although the public service corporation is required to be impartial under the terms of its charter, 21 per cent of viewers felt that BBC1 unfairly favoured the Tories and a further 15 per cent said the same of BBC2.
Only 7 per cent said ITV was biased toward the Conservatives and just 3 per cent thought it was the case with Channel 4.
By contrast, 7 per cent felt BBC1 showed bias towards the Labour Party and only 4 per cent said the same of BBC2. Seven per cent also believed ITV and Channel 4 unfairly favoured Labour.
The findings are part of an annual poll of 1,000 viewers, carried out last year by the commercial television regulator, which is required by the 1990 Broadcasting Act to research public opinion.
The overwhelming perception of bias towards the Conservatives, especially on BBC1, will add pressure to the corporation in the run-up to the general election.
It set up a political monitoring unit last year after attempts by Alistair Campbell, Tony Blair's press secretary, to ensure the Labour leader's keynote speech at the party conference was the lead news item over the OJ Simpson murder verdict.
Viewers also spoke out about the bias against different professions and groups of the population they believed that all the terrestrial channels showed in their news and current affairs programmes.
They thought most bias was shown against single parents (27 per cent) with the unemployed (24 per cent) and trade unions (23 per cent) close behind. The disabled were also on the list (16 per cent), as were social service employees (18 per cent) and women (11 per cent).
The commercialisation of the BBC is to continue with the creation of BBC Films Ltd.
The proposal must be agreed by the BBC board of management, its governors and the Department of National Heritage, but senior insiders believe it will get the green light, possibly within weeks.
The business plan suggests making 10 feature films a year with each film shown on the BBC after release on video, in cinemas or even on pay- TV.Reuse content