Professor Philip Lane:

As the Deputy just indicated, which is consistent with our data, many first-time buyers put down fairly big deposits compared with the value of a home. The fraction of first-time buyers who were, or are, constrained by the 10% deposit is going to be limited. This is true of any subsidy scheme. It is the conundrum of whether one is able to target those who need a subsidy or, if one sets out a rule, whether it will include many more people who already have a capacity to meet our deposit requirements.

That is an inevitability of all subsidy schemes. It is one reason cost-benefit analyses of schemes are a good idea to work out the ratio between those who alter their circumstances against those for whom it is essentially a windfall and an extra receipt for income.