A leading Conservative has described the arrest of Damian Green and the raid on his parliamentary office as acts that could have been committed under President Mugabe’s regime in Zimbabwe.

Michael Portillo, the former minister who is now a well-known political commentator, said he could not understand how Scotland Yard had ever considered it necessary to arrest the Ashford MP.

His denunciation of events surrounding the arrest of the Kent Conservative MP were made during a speech to Kent journalists in Maidstone.

Mr Portillo said: “To me, the arrest of Damian Green, who had committed nothing more important than embarrassing the Government, indicates a really alarming issue. Before our startled eyes, we have lurched to becoming like Zimbabwe. The anti-terrorist police turned up in his office. How that happened, I cannot imagine.”

He went on to criticise Scotland Yard for sanctioning the arrests, saying: “If the police had read newspapers, what Damian Green was trafficking in was information liable to embarrass the Government, which wanted to obscure the information.”

It was “beyond my imagination” how the police had ever been given permission to raid the office of an MP, saying it illustrated Gordon Brown’s indifference to the institution of Parliament.

However, he welcomed the strong statement from the Director of Public Prosecutions Keir Starmer which argued that the material leaked by the MP could be construed as being in the public interest.

Meanwhile, the Crown Prosecution Service has revealed it spent more than £4,000 taking external legal advice from two expert lawyers about whether to bring charges against the MP. But it has refused to say how much money it spent on the investigation.

In data disclosed to the Kentish Express under the Freedom of Information Act, the CPS said it took advice from Gavin Millar QC, a leading media lawyer specialist and James Lewis QC, a specialist in Parliamentary privilege, who charged £4,036 for their advice.

But it said it would take too long to set out other costs related to the investigation because it would involve a “significant diversion of resources”.