Andy Coulson is set to be arrested this morning on suspicion he knew about phone hacking at the paper (Photo: David Moir, Reuters)

Andy Coulson, the former Downing Street spin doctor, will reportedly be arrested on suspicion that he knew of or was involved in the illegal hacking of phones while serving as the editor of the soon-to-be defunct News of the World.

Police yesterday informed Coulson of their intention to arrest him on Friday morning, according to The Guardian. Confirming reports that emerged earlier in the week, the paper said that at least one more senior journalist would be arrested within days.

The speed with which the scandal has escalated has forced the Metropolitan Police to step up a gear. Sue Akers, the senior detective leading the police investigation into phone hacking, said that the police were working to contact nearly 4,000 individuals whose phones may have been hacked.

Coulson was the News of the World's editor between 2003 and 2007, having earlier served as the deputy editor under the leadership of Rebekah Brooks, now the chief executive of News International. Three journalists were hauled in by police earlier this year in connection with phone hacking, but Coulson's arrest would be the most significant and high-profile to date.

It would also add to the already considerable pressure on Prime Minister David Cameron, who hired Coulson as the Conservative Party's communications chief after his resignation from the News of the World in 2007. During an emergency Commons debate on Wednesday, Labour's Ed Miliband reiterated long-standing accusations that the decision to bring Coulson on board was "a colossal error of judgement".

Coulson resigned as Downing Street's director of communications in January, claiming that questions about his role in phone hacking were drawing attention away from the Government, but denying once again that he knew of illegal activities taking place under his leadership.

Renewed pressure on Coulson this week came after it was revealed that News International had handed over evidence suggesting that under his leadership, the News of the World authorised illegal payments to police in return for sensitive information.

His expected arrest adds to a tumultuous week in which the phone-hacking scandal exploded onto the front pages and triggered widespread public fury. The paper's closure due to the affair was announced by James Murdoch on Thursday afternoon.

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