Prime Minister Scott Morrison and Treasurer Josh Frydenberg (Image: AAP/Lukas Coch)

At $130 billion, it's the biggest backflip in Australian political history, and the most welcome.

In less than a week, Scott Morrison has gone from calling an economy-wide wage subsidy scheme "dangerous", claiming it would require a whole new payments system and couldn't be done quickly, to announcing $130 billion over two quarters, to be delivered from the start of May via the tax system. And it's more comprehensive in some areas than the UK wage subsidy scheme, though less so in terms of the proportion of wages subsidised.

All the problems of such a scheme are present. It will create perverse incentives, there are arbitrary and perhaps unfair thresholds (especially around casual workers), there are opportunities for gaming.