Here is a bit more detail about how Help to Buy ll will work after it is launched by the Treasury on Tuesday.

I am told that the Treasury has told the banks it will charge them a supposedly "commercial" rate of about 0.9% for insuring up to three-quarters of the first 20% of losses on mortgages for homebuyers who cannot afford to provide a big deposit.

And apparently that 0.9% applies to the whole loan, not just the insured proportion.

The charge is necessary to prevent Brussels ruling the scheme as illegal state aid.

But it implies that Help to Buy ll could be quite a money-spinner for the Treasury. The government could receive annual revenues of just under £12bn a year (see update below please), if it were to provide guarantees on the maximum £130bn of mortgages it estimates that it could insure.

As one banker said to me: "Unless the mortgages go sour, the Treasury will clean up."