A predictable row has erupted about the arrest of the Conservative immigration minister Damian Green as part of the Metropolitan Police's inquiry into information leaked from the Home Office.

Many Tories have accused the Labour Government of turning a blind eye to the humiliation of a rival. Voters, by contrast, may wonder what the fuss is about: why should MPs be above the law? It's easy to sympathise with this, especially after Tony Blair's cronies faced a similar experience in the cash for peerages inquiry.

But the Damian Green case is disturbing. What on earth were anti-terrorism police officers doing raiding parliament and arresting an MP over a leak? This is little short of an outrage. It confirms my long-standing view that anti-terrorism and security legislation is all too easily abused. (Remember Walter Wolfgang, the 82 year old thrown out of the Labour conference in 2005 and held under the Terrorism Act – for heckling?)

Leaks have long been a source of sustenance for opposition parties and an irritant for governments. I don't know whether Damian Green's activities deserve praise for keeping the public informed or criticism for undermining good government. But it is sobering to think that Winston Churchill may never had become prime minister in 1940 had such a draconian regime been in force in the 1930s. Churchill's campaign against Britain's poor readiness to defend itself against Nazi Germany was informed by a series of secret briefings by Ralph Wigram, a senior civil servant appalled by the incompetence of the MacDonald and Baldwin governments. Sir Martin Gilbert, Churchill's biographer, writes movingly about Wigram and Winston in his wonderful memoir, In Search of Churchill. Churchill survived to lead Britain to victory, describing Ralph Wigram as a great unsung hero.