The multi-million pound 2012 giveaway but who pays?
But he is still struggling to get the private cash to pay for it.
I understand Mr Johnson is looking for £2m from the private sector to pay for the 75,000 extra tickets he is buying in addition to the 50,000 he receives automatically from the organising committee for the kids' programme.
I've learned he went close to striking a deal last week with one leading London business but the negotiations broke down because the Mayor wanted too much money.
So, at the moment London council taxpayers will be paying for the tickets.
The Mayor is hoping one in eight children will get a chance to get their hands on the free tickets. They qualify by achieving a goal at school as part of 2012's Get Set programme.
There is a serious hurdle to overcome for the Mayor in getting the private sector to pay for all this. Any backer is going to want publicity for the scheme. But that is unlikely to go down well with official sponsors.
The backer will look like an official sponsor when it won't be.
So, how about copying an idea from the 2008 Beijing Olympics? China funded its magnificent Aquatics Centre by asking thousands of Chinese businessmen abroad to pay towards the project.
How about asking hundreds of businesses and organisations across London to pay for the scheme?
They would receive small recognition for their support but it wouldn't be so dramatic that it would look like they were ambushing the Olympic marketing campaign?
Or is it right that council taxpayers simply pay for all of this?