BT pension trustees have asked the High Court to determine how much of the firm’s final salary pension fund is guaranteed by the state. The taxpayer could be liable for between £7.3bn and £22.8bn if the company went bankrupt, court papers said yesterday. The case aims to clarify whether employees who joined the scheme after the firm was privatised in 1984 are protected, and a legal decision could help BT decide how to approach its £40bn pensions black hole. BT supports the trustees in the case, but believes the state should guarantee three-quarters of the liability. A ruling is expected in October.