"I don't think BT want to come out and say what the actual numbers are, it would be share price suicide and it also makes paying dividends difficult."
The trouble is that any financial analyst worth their salt will take into account pension risks when building a valuation model for a company.
So the financial analyst will do some digging of their own, and some data is also available on platforms such as Reuters and Bloomberg (which, in terms of pensions, ultimately comes from the company's accounts).
So to take an example from one such platform, there is an item called "Net Asset / Liability Recognized on Balance Sheet (Pension)" which is described as "This data item represents the net value related to pension plans recognized on the Company's Balance Sheet.".
And if you look at BT on that platform, 12months to March 2016 shows a figure of approx (-6bn) and 12 months March 2017 shows a figure of approx (-9bn)