The police faced fresh accusations of lobbying after a police officer from Scotland Yard sent an e-mails to Labour MPs denying it operated a "shoot-to-kill" policy.
The unsolicitied messages defended the tactics used by the armed officers who killed Jean Charles de Menezes, an innocent Brazilian electrician, in July.
Following the storm over attempts by chief constables to influence last week's vote in the House of Commons on locking up Islamic terrorist suspects without charge for up to 90 days, an all-party committee of MPs is to investigate whether the police are becoming politicised.
The e-mails were sent by Nick Williams, the acting inspector at the Metropolitan Police's Diamond Support Group.
He told MPs that the "Operation Kratos" tactic used against suspected suicide bombers was "not a shoot to kill policy".
He said: "In the modern era of terrorism, it is essential police are able to deploy appropriate tactics when necessary, whilst acting fully in accordance with the law, in order to safeguard the public against mass murder.
"No police action is targeted against particular communities - we only seek to target suspected criminals. In doing so, we aim to protect society as a whole."
John McDonnell, the chairman of the Campaign Group of Labour MPs, said: "It looks as though is another example of lobbying to try to influence MPs' attitudes before any future inquiry into the [de Menezes] shooting in south London.
"It is surprising behaviour. It smacks of the Met entering into political sphere." Scotland Yard denied the e-mail amounted to lobbying, saying it merely drew attention to material already in the public domain.
An investigation by the House of Commons Home Affairs Select Committee will focus on the case for 90-day detention, but MPs will also question senior police officers over their attempts to influence last week's vote.
James Clappison, a Conservative committee member, said: "They came into the political arena and contacted MPs on a very sensitive issue. We have to look at that."