British telecoms operator BT is facing a claim for almost £600m lodged by a consumer campaign group, which says the company failed to compensate fixed-line customers, many of them elderly, for overcharging. 

The group, Collective Action on Land Lines (CALL), says the former monopoly failed to make up for increasing prices for customers over several years even though costs for providing the service were falling. 

In 2017, telecoms regulator Ofcom raised concerns about the price BT had charged landline-only customers, and the company agreed to reduce its landline prices by £7 a month. 

However, CALL said BT had not properly addressed past overcharging. 

Its £589m claim, filed with the Competition Appeal Tribunal, sought payments of up to £500 for each of 2.3 million BT customers. 

The group said it was also seeking compensation for customers who took both a broadband service and a BT landline, but not as a package, and were excluded from BT's 2017 price cut. 

BT said it strongly disagreed with the claim. 

"We take our responsibilities to older and more vulnerable customers very seriously and will defend ourselves against any claim that suggests otherwise," it said in a statement.

The claim went back as far as 2015, the earliest starting point under legal rules, CALL said.