For the want of a horseshoe...
The Guardian calculates that to achieve Frank Field's objective that the abolition of the 10p tax rate would not come into force "until the chancellor of the exchequer lays before parliament a statement that, in his opinion, measures have been taken to ensure that no person is worse off by reason of the person's income not being sufficient to secure that the effect of the abolition of the starting rate is offset by the reduction of the basic rate" would only cost £700 million.
£700 million is small change in terms of Government budgeting. It's the running costs of a couple of small London borough councils or the construction cost of a single new hospital.
But to the people whose incomes are affected, who are already struggling to make ends meet, it would make a big difference.
The cost of not compensating them is also one that would be paid reputationally by the PM in terms of loss of the moral authority he rightly holds as a campaigner and combatter against poverty at home and abroad, and one that would be paid politically by Labour as a Party in terms of lost trust not just amongst the people affected, but also amongst better-off voters who support Labour because of our redistributive values.
£700m isn't a lot to find somewhere down the side of a proverbial sofa in HM Treasury to make life a bit easier for people earning less than £18,000 a year, and it isn't a lot to find to restore people's faith that the Government's decisions are guided by an explicitly Labour moral compass.