Of all the things conceived and delivered by the London Labour movement, it is the work to implement the Freedom Pass that makes me most proud.
The future of the Freedom Pass has given Labour members in London an important decision to make about the future direction of policy in the city.
An honest difference of view between myself and Oona King has opened up over this issue at members' debates in Croydon and Brent. Asked if the Freedom Pass should be means-tested, Oona has argued  that "If there is a choice, then I want the money to go to the poorest, not to pay for the richest like Prince Charles to go free" and "If you are the mayor and you have got less money coming in, you need to ensure the average pensioner can have the same experience or better than those richer ones . . . you need to accept means testing."
I disagree. On such a fundamental question, it is necessary to give a clear answer: that the Freedom Pass is safe. If I am selected as Labour's candidate and then elected as mayor, I will oppose any attempt to means-test the Freedom Pass. I will defend the concessionary schemes.
I never expected to hear in a Labour mayoral selection that we should consider means-testing the Freedom Pass. It is a catastrophic mistake, a gift to our opponents, including Boris Johnson. We must have a clear bottom line -- and a universal Freedom Pass should be part of it.
This strikes at the heart of electability. A London Labour candidate going into an election with a question mark over the Freedom Pass, such as being open to the idea of means-testing it, would damage Labour . Either Boris Johnson will use it as a stick with which to beat Labour, posing to the "left" of the Labour candidate, or it will open up territory that assists those who want to erode travel concessions.
In both circumstances, it is a direct blow against Londoners and would make it harder to win.
I will oppose any attempt to means-test the Freedom Pass and defend the Freedom Pass.
The Freedom Pass unites people across London. It is particularly crucial in the outer boroughs, one of the areas where its take-up is greatest. The latest figures  show 51,691 Freedom Passes issued in Barnet for older Londoners and 5,903 for disabled people, for example. Another 43,791 in total have been issued in Bexley, 63,671 in Bromley and 48,827 in Havering.
Older people make up a significantly high proportion of voters  and are therefore vital to our support.
There is already concern that the national bus concessionary scheme may be under threat  from government cuts.
It is not the super-rich who would be affected by means testing. You are unlikely to find billionaires or members of the royal family taking advantage of the Freedom Pass. To save any meaningful amount of money, the cut-off point for the means test would not be for multimillionaires, but for individuals on much lower levels of subsistence.
The cost of administering means testing could only be offset by placing the cut-off way below the richest. The question for anyone toying with the notion of means-testing something like the Freedom Pass is: where would you draw the line?
And why stop at the Freedom Pass? There are many universal services and benefits that could also be threatened, such as free bus and tram travel for under-18s -- which the Tories have already previously tried to remove.
It is a more profound issue even than that. Some services are best delivered universally or with universal concessions for key groups. That ensures broad support for services -- such as public transport -- that would otherwise be much easier to cut by right-wing governments.
The more widely people use public transport and see the benefits, the more the city moves freely and the biggest number of people possible will have a stake in maintaining those services.
The Freedom Pass is so popular with older and disabled Londoners and their families that Boris Johnson was forced to adopt our plan to extend the Freedom Pass to 24-hour operation (though he has failed to secure its 24-hour operation on many rail services).
For Labour to succeed in 2012, it must have a strategy for winning based on protecting Londoners from the combined assault of the economic situation and a government whose policies will worsen its impact.
That is why I will not toy with ideas like means-testing the Freedom Pass, and why I will support other universal services and benefits that make our society fairer and stronger.
Ken Livingstone was mayor of London between 2000 and 2008, and is currently campaigning to be Labour's candidate in the 2012 London mayoral election.