Downing Street has angrily denied claims that members of its staff hacked in to the BBC's computer network in a bid to influence news coverage following Labour's victory in the 1997 general election.

The allegations arose following the recent publication of a book by BBC world affairs editor, John Simpson, in which he claims that reporters would be lobbied by Downing Street before reports were even broadcast.

Although it is thought that the BBC conducted an investigation into the hacking allegations following the Labour victory, no evidence was found. But Simpson told The Guardian that "several colleagues are morally certain that it has happened".

In his book, News from No Man's Land, Simpson said that on numerous occasions when he or a colleague used the newsroom computer to write up a script for the next bulletin, Downing Street would call up before the broadcast and lobby the correspondent on a point or two.

Nothing came of the 1997 investigation, which focused on former BBC employees who might still have had access to password-protected parts of the network, but the newsroom is said to have improved security following the investigation.

Simpson alleged that the tactics were part of a bid to pressurise the media into more favourable coverage of Labour's policies.

The government has slammed the allegations as "complete rubbish", but David Davis, shadow secretary for the Office of the Deputy Prime Minister, has said he will demand the publication of the BBC's internal report.