For all married couples: £3.2 billion
For married couples with dependent children or in receipt of Carers Allowance: £1.5bn
For married couples with children under 6: £0.9bn
For married couples with children aged 0-3, the most important years for a child’s development: £0.6bn
It's the final option, costing £600 million, that the Tories are said to be interested in – although they regard this more as initial step before extending the tax break to all married couples as soon as the public finances allow.
At which point, it's worth returning to the CSJ's incredibly important report on dynamic benefits. Dave 'n' George were said to be put off the reform package it proposes because of its hefty, £4 billion-or-so price tag. But, as I pointed out in this post, the CSJ set out a range of different costings in that report too. Might the Tories sign up to one of those cheaper options for benefit reform? Watch this space.