Convincing the rebels
It was meant to be ministers' trump card.
The hole in the Royal Mail's pension fund is so big that they've been warned the company is "balance sheet insolvent" and postal workers wouldn't get their full pension if the scheme was wound up.
Ministers released the letter from the pension fund trustees on the eve of today's demonstration by the postal workers union against part privatisation.
The letter's message is clear: "How can a union and Labour MPs protest when we're coming to the rescue of the posties pension fund at the very moment many want us to scrap cushy public sector pensions?"
Rebels may reply "we'll take the pension protection without the privatisation, thanks".
By starting this bill in the Lords, ministers have given themselves a couple of months to try to win the argument with almost 140 rebel Labour MPs that the taxpayer cannot be asked to foot the bill for reforming Royal Mail as well as paying its pensions.
The problem they face is that numbers have almost lost their meaning these days - after all, what's £7bn at a time we're spending £1.3tn on bailing out the banks?
PS Forgive the shameless plug, but you can catch up on the first of my programmes, the Prime Ministers, by listening here.