Inaccurate lists of vulnerable people led to delays in responding to storms, with staff sent to non-existent homes and a customer who had died years earlier, a committee has heard.

Giving evidence to an inquiry on storms Bert and Darragh, which hit Wales late last year, Carmarthenshire council described utility firms’ priority customer data as severely flawed.

The council told the Senedd’s climate committee the lists were inaccurate, out of date, and incompatible with NHS and social care definitions of vulnerability.

In written evidence, the council said this resulted in staff being deployed to screen the sheer volume, comparing thousands of names with council and health board records.

The council warned: “This caused unnecessary delays and on several occasions diverted operational staff away from their responsive work … to check addresses which did not either exist or in one case, the customer had passed away years before.”

Appearing before the committee on 6 March, Paul Ridley, the council’s civil contingencies manager, called for consistency in the interpretation of vulnerability across all agencies.

Ainsley Williams, director of infrastructure at the council, pointed to initial problems due to concerns raised about data sharing and GDPR.

He added: “It still needs wider awareness amongst organisations that they can do that and must do that in an emergency.”

Ian Christie, managing director of water services at Dŵr Cymru Welsh Water, said: “There is work to be done on joining up all vulnerable customers because we all have individual priority services registers with all different definitions of what makes a customer vulnerable.”

Mr Christie told the committee that GDPR “unfortunately cuts through everything”.

He said: “One of our biggest issues is trying to explain to a customer: just because they’ve registered … with another agency, that doesn’t automatically update to our priority services.”

Liam O’Sullivan, director of ScottishPower Energy Networks which owns the north Wales network, said customers are contracted every two years to check information is up to date.

“It’s very difficult at times because it’s an ever-changing picture,” he told Senedd members.

The Conservatives’ Janet Finch-Saunders warned of huge issues with priority registers.

Ms Finch-Saunders said: “I can’t for the life of me – now with digital technology – understand why we haven’t got one list that is used by the fire [service], health, you name it.”

She raised January’s burst pipe which left 100,000 people in north Wales without water, with the number of customers registered as vulnerable doubling to 7,500 in a few days.

“That shows there’s some weakness in the system,” she said.

Labour’s Carolyn Thomas questioned why Anglesey council was only provided with a register at 9pm on 9 December, more than 24 hours after storm Darragh’s peak.

Mr O’Sullivan said of the approximately 70,000 people who live on the island, 17,000 are on the priority services register.

Mr Christie explained a task-and-finish group has been set up by Huw Irranca-Davies, the deputy first minister, to look at trying to resolve the issue of one common list.