BT £9bn hole: How much could fall on taxpayers?
The hole in BT's pension fund is a jarring £9bn, according to the formal three-yearly valuation.
That's the largest pensions deficit ever announced by a listed British company, although some analysts thought the gap could be even higher.
For example, John Ralfe - the pensions expert - thought the deficit was closer to £11bn.
Even so, £9bn is a big number. And under pensions law, this is a formal debt of the company and has to be paid off.
There are two ways of looking at this debt.
If you're a BT shareholder, it is a massive and worrying drag on BT's ability to invest, grow and pay dividends.
If you're one of 340,000 current or future BT pensioners, the hole would raise concerns about whether the business has the wherewithal to honour its financial commitments to you.
That said, what will particularly trouble BT's owners and employees is that the Pensions Regulator has substantial concerns with BT's plan to fill the hole.
BT has agreed with the trustee to pay £525m per annum into the fund for three years, and then £585m, increasing annually by 3%. Adjusting for inflation, BT would be paying in £533m each year.
That is certainly not a trivial contribution. But it won't eliminate the deficit for 17 years, which - as John Ralfe points out - is longer than the 10-year repayment schedule which the regulator normally prefers.
However, BT pensioners have protection not normally afforded to members of private-sector schemes: when the company was privatised in 1984, the government gave a commitment that it would honour the pension liabilities to those who belonged to the scheme at the time, in the event that BT were ever to go bust.
The degree of protection that provides to today's scheme is not 100% clear. BT's trustees believe that it means that the state - that's us, taxpayers, by the way - would be on the hook for just under 75% of the scheme's current liabilities.
To end any uncertainty, the trustees have taken the issue to court, for clarification of the extent to which taxpayers would be liable, if the worst came to the worst.
Were the court to rule that taxpayers are standing behind the lion's share of the scheme's liabilities, that might persuade the regulator that BT's £533m annual payments into the fund are sufficient.
On the other hand, the regulator might look at today's third-quarter results from BT - and note that the business is recovering faster and stronger than BT thought would be the case a year or so ago.
For example, BT now expects to generate free cash flows of £1.7bn this year, 70% greater than its initial prediction.
And although BT has slashed its dividend, it is still planning to pay dividends.
It is not implausible that the regulator will eventually rule that BT should work more for its pensions and less for its shareholders - which would imply that the company would have to pay even more into the pension scheme.
That said, the regulator would not want to impose pension payments that were so large that they hobbled BT, because that would damage pensioners as well as shareholders.