Leading article: Competent leadership badly needed

The scandal of the arrest of the Shadow immigration minister, Damian Green, continues to reverberate. Arresting MPs (not to mention raiding their offices in the House of Commons) is no small matter in a democracy. The affair must be treated with the highest seriousness by the Government. Before anything else we need an official statement detailing exactly what ministers knew before the raid went ahead. Otherwise, poisonous suspicions that the police have been used as a political tool will continue to fester.

This affair also shines an unforgiving spotlight on the present sorry condition of the Metropolitan Police. The past three years have been truly wretched for the reputation of the nation's biggest force. It began when Sir Ian Blair became Commissioner in 2005. One of his first decisions was to lobby MPs in support of a Government Bill to detain terror suspects for 90 days without charge. This opened Sir Ian up to accusations of attempting to turn the police into a political player – accusations that have never been convincingly dispelled since.

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The Menezes catastrophe, when officers shot dead an innocent Brazilian man at Stockwell Underground station, believing he was a suicide bomber, exposed significant internal discord at Scotland Yard. The Deputy Assistant Commissioner, Brian Paddick, questioned his boss's account of the Met's operations on that dark day and subsequently resigned. More recently, there have been embarrassing accusations from Tarique Ghaffur, Britain's most senior Asian officer, that Sir Ian Blair, motivated by racial prejudice, blocked his career progress. Whatever the truth of that business, it cemented the impression of a deeply divided leadership. And now we have this terrible misjudgment from the acting head of the Metropolitan Police, Sir Paul Stephenson, in sanctioning the arrest of Mr Green.

Today is the deadline for applications for the vacant post of Commissioner. A decision will be made on Sir Ian's permanent successor early next year. The Government needs to choose very carefully. The Metropolitan Police is a ship that urgently needs the steadying hand of an astute and competent leader.