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Former head of MI5 Eliza Manningham-Buller today joins an increasingly long list of "formers" and "exes" who have publicly condemned the so-called "War on Drugs" as a "dead end".

This afternoon in the House of Lords there will be a former President (Switzerland's Ruth Dreifuss), a former chief of the US Federal Reserve (Paul Volker) and a former Chancellor of the Exchequer (Nigel Lawson).

They will be among many other retired establishment figures lining up to say that we need to launch a global and national search operation for a workable alternative to prohibition.

The question that leaps out, of course, is why didn't any of these people make their argument before they retired from the day-job?

A glance at the members of the Global Commission on Drug Policy, which today presents its manifesto in the Palace of Westminster, reveals the same story: four former national Presidents, a former US Secretary of State (George Schultz) and a former UN Secretary General (Kofi Annan) are among hundreds of thousands of signatories to a petition calling for health-oriented, cost-effective drugs policies based in scientific evidence and human rights.

But why didn't they say anything before?

The answer, it seems, is that the towering walls of political orthodoxy made it impossible.

Eliza Manningham-Buller likens it to the Emperor's New Clothes: "Those politicians and commentators who may recognise that, at the very least, there are serious questions about the efficacy of current policies, go quiet or retract when faced by the crude assertion that any other policy would do corrosive and irreparable harm."

Justin Webb's question to me on the BBC Today programme this morning was a good one. How, he asked, will Lady Manningham-Buller get round the problem of a political and media establishment that does not think there is anything to be gained in opening a debate around the policy of prohibition?

Her answer is to detoxify the politics by creating some all-party forum, akin to a Royal Commission, that can discuss the issues without fears of vilification. But I come back to my question - why do we need to hide this critical debate behind the neutral-coloured curtains of a commission full of former this's and ex that's?

It would seem to be a weakness of our democracy (and political conviction) that we are denied a rational and candid examination of drugs policy because front-bench politicians are terrified of being labelled as "soft" or "liberal".

Lady Manningham-Buller makes an important point when she asks why we don't trust the public on this subject. Do politicians too easily assume that voters will turn against them if they question the long-held orthodoxy on drugs?

Or might they gain respect by demanding, as the former spymaster puts it, whether we continue "on the same well-worn track which will lead to the same dead end".

The government says it is "opposed to the legalisation of drugs and to decriminalisation for personal use because drugs are harmful and no-one should take them". There is nothing in the wind to suggest any interest in debating the policy of prohibition.

But I bet there are some senior figures in the heart of government right now who secretly share Lady Manningham-Buller's concerns. Will we have to wait until they, too, are a "former" or an "ex" before they say anything?