What do spies do when they retire? Write novels, garden, spend time with their family - or, in the case of one former MI5 head, call to legalise drugs.

On Thursday Baroness Manningham-Buller made headlines when she said it was time to look at evidence-based drug policy. She has joined the ranks of the All Parliamentary Group on Drug Policy Reform, who want David Cameron to set up a commission looking at the issue.

Manningham-Buller isn’t the only former something who believes the war on drugs is not working. Bob Ainsworth, who was once the Home Office minister with responsibility for drugs policy, injected some new life into the debate last December when he said it was time to decriminalise them - including cocaine and heroine - and take them out of "the hands of criminals".

"We must take the trade away from organised criminals and hand it to the control of doctors and pharmacists," he said.

Nearly 11 months on and Ainsworth “absolutely” stands by his calls.

While he was in the Home Office, the Labour MP said he achieved only "10% of what I would have wanted", downgrading cannabis and making it legal to prescribe heroin - outside of government he can go further.

"This will move, one day, and it's impossible to say when and it will probably come quite suddenly. People will think that the war on drugs has been a failure. Progress has been made but I'm not sure it's imminent."

So why do former politicians speak out? Transform, a pressure group campaigning against the war on drugs, even have a phrase for the phenomenon - “retirement syndrome”.

For Ainsworth, Manningham-Buller was “absolutely right” to only speak out after leaving office - and so was he. "You cannot do that kind of job and be a free spirit. You are part of government and have to go with its responsibilities. You can resign and be totally free to say what you like or you can continue and you can try to move policy to the degree that you can gain consensus."

Danny Kushlick, Transform’s head of external affairs says it’s “a question of time” before that consensus builds; First come the former ministers and civil servants, then come the current ones.

“Basically it's a taboo issue until you reach the point where is comes to the forefront. Both the presidents of Colombia and Mexico have been making, as incumbents, statements against the war on drugs.”

The Home Office has always maintained decriminalisation of drugs is too simplistic and does not address the harm of taking drugs - but Kushlick believes it’s a matter of time before drugs are legal - in part, due to the global economic crisis: “We're looking at 2020, drugs being legalised within a 10 year time frame.

“The global economic crisis is producing scrutiny of lousy expenditure. Spending £100bn a year on the war on drugs and then even more clearing up the mess from it isn't tenable.

“You can fight expensive wars when you're rich but not when you're poor”.

Kushlick points out that prohibition in America ended in the context of the great depression in the 1930s - and the same thing could happen now.

Not everyone shares his optimism. "Crises are not usually progressive, and progressive policies are not usually made as a result of crisis”, Ainsworth said.

And some think we’re having the wrong argument altogether. Leo Barasi, of the UK Drug Policy Commission says drug policy has become “polarised” between decriminalisation and prohibition - making the debate “toxic” for senior and ambitious politicians.

“The drugs market is changing with new ‘legal highs’ and we’re seeing more evidence of what can work from other countries that are trying different control systems and ways to help people with drug problems.

“We should recognise that there are lots of ways we can control different kinds of drugs and take action against suppliers. It’s important we allow policymakers to look at the evidence on how we can best reduce the damage drugs can cause”.