Senior figures at the BBC World Service have expressed concern to the domestic news division that coverage of the Zimbabwe elections has been driven by a "colonial" agenda, potentially causing damage to the corporation's reputation for impartiality.

Particular anxieties have been expressed about the tone of coverage on Radio 4's Today programme and about a Correspondent documentary in which the former Observer journalist John Sweeney smuggled himself into Zimbabwe in the boot of a car.

There has also been concern about the frequent BBC claim that it is banned from Zimbabwe. While it is true to say that BBC correspondents have been refused entry, a number of African World Service reporters are working legitimately there.

After one of the reporters appeared on Radio 5 Live yesterday, the BBC changed its policy. Radio news will now use terms such as "severely restricted", while TV bulletins will say either that "BBC television is banned from Zimbabwe" or "BBC correspondents are banned".

Sources at the World Service, who did not wish to be named, told the Guardian that concerns had been expressed by senior executives at Bush House in London to Adrian van Klaveren, the head of BBC newsgathering, and to Steve Mitchell, the head of radio news.

There were worries about the tone of coverage on the Today programme, which, according to some at the World Service, has made a conscious attempt to "illegitimise" the Robert Mugabe administration with the use of pejorative terms such as "regime" and adjectives such as tough, fierce and brutal.

While these were acceptable when used by correspondents on the scene, they were being used by Today presenters in the introduction to reports, and during news bulletins.

The sources did not attempt to suggest that Mr Mugabe was without fault, but they pointed to worse abuses committed by governments in Liberia and Congo. Elections in Congo were held last weekend amid allegations of huge electoral fraud, yet did not feature prominently on the domestic news agenda.

It is suggested that the interest in the Zimbabwe elections is being driven by the "residual British interest and the presence of white farmers", according to one Bush House source. Another said the agenda was characterised by "latent and unwitting colonialism".

There has also been concern about the prominence being given to the Zimbabwe elections on the World Service's main news programmes, the World Today, World Update and Newshour, which are broadcast to tens of millions of listeners around the world.

Several sources suggested the agenda was more "foreign" than "international": that the story was being seen from a London-based rather than a global perspective.

The Correspondent documentary, broadcast on the World Service as well as BBC2, caused upset because Sweeney appeared to suggest it was necessary to hide in a car to interview the opposition leader, Morgan Tsvangirai. In fact, Mr Tsvangirai has been interviewed many times by different BBC outlets, even appearing in person at Bush House.

The BBC said it was committed to reporting extensively from Zimbabwe. A spokesman said: "Clearly the Zimbabwe elections are one of the biggest international stories at the moment, and of course we are going to cover it extensively. In terms of the tone, we are wedded to being impartial and careful, but clearly when there is such huge worldwide concern about allegations of intimidation and violence, that will be reflected in coverage.

"The BBC has three bureaux and many correspondents in Africa and we probably cover more on African affairs than anyone else. We have done Congo, Malawi, Liberia and Nigeria, all on mainstream BBC1 bulletins."