The hearing is expected to last for three days, with the ruling likely to be given early in 2019.

In January the High Court ruled that BT could not change the index used to calculate pension increases for around 80,000 scheme members in Section C of the BTPS from the Retail Prices Index (RPI) to the Consumer Prices Index (CPI).

CPI is generally lower than RPI, so switching the index for increasing the pensions of those in Section C would reduce their collective expected future retirement incomes by hundreds of millions of pounds.

The High Court ruling was that it was not currently possible to interpret the rules of Section C of the BT Pension Scheme as allowing BT to make this change. It was based on the judge’s view that RPI has not, at this time, “become inappropriate” for the purposes of uprating pensions.

Prospect national secretary Noel McClean said: “Prospect strongly supports the High Court’s decision and is disappointed that BT has chosen to appeal that judgment.

“BT seems determined to keep this case going because the potential pay-off is so high. However any return to BT would come straight out of the pockets of BT pensioners and current BT employees. That is no way to treat people who have given so much to the company.”

• The BT Pension Scheme was closed for future accrual from 1 June 2018. CPI is already used to calculate increases for members in Sections A and B of the BTPS, who joined the scheme up to 1986. Section C covers joiners from 1 April 1986 until the scheme closed to new entrants on 31 March 2001.
• See earlier web story here