"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."
It should also be noted that the very reason (well, one of the big reasons) the pension has not caused "share price suicide" is because BT continues to pay dividends.
Professional portfolio managers will often have remits which constrain what they can invest in.
So, for example, someone managing investments relating to a company's pension scheme might have a conservative mandate (e.g. investment-grade bonds only, FTSE100 only). You might then be further restricted if you are given a mandate of "income" rather than "growth", which would restrict you to dividend paying shares (and/or bonds).
As well as those managing specific portfolios, you also have the whole industry of funds (active and passive) which any "joe" can buy ... those funds will have specific mandates too which constrain them.
As a result, given you have a limited shopping list, companies such as BT can be often seen as one of those "back of the cupboard" buy and forget companies.
If, for example, BT dropped out of the FTSE100, or their ability to pay dividends in a reasonably sustainable manner was called into question, then *THAT* is when you would see the *REAL* "suicide", because all the professional managers would start pulling out very swiftly indeed as they would no longer be permitted to hold BT shares under their mandate.