Thames Water could be told to return £100m to customers after coming in last place in Ofwat’s customer service report for four years running.

The report combines scores on customer satisfaction for handling issues and the number of complaints each company received. The combined figures provide a score out of 100 for the year 2018-19.

Anglian Water topped the table for the second year running, followed by Portsmouth Water, which had the highest proportion of customers who felt their query was resolved.

Anglian Water received a score of 90, Portsmouth Water 89.1, while United Utilities, South West Water and Bournemouth Water all scored 87.6.

At the bottom of the table, Thames Water scored 75, and Hafren Dyfrdwy 78.4.

This year’s results also showed improved scores from Dŵr Cymru, with Southern Water maintaining the improvement it showed last year.

Although Southern Water remained a poor performer, it has increased its score by 7 points since 2015. The number of written complaints Southern received has reduced by 27 per cent in the same period.

Each water company’s overall score since 2015 results in either a financial payment or penalty. Ofwat consulted on the range of payments as part of its 2019 price review draft determinations in July 2019.

Including the scores published today, those proposals mean Anglian Water would receive an extra £36m in its price review settlement, while Thames Water’s would be reduced by £100m.

David Black, senior director at Ofwat, said: “We expect companies to put customers at the heart of their business. Those like Thames which achieve persistently low scores need to give this area of their performance more focus. Until they do so they will continue to face penalties and pressure to pay more attention to understanding and meeting their customer needs.

“Whilst it is encouraging to see the top performers doing even better than last year, we are disappointed to see a drop in the overall average industry score, with the worst performers failing to show improvement.

“We expect companies to benchmark themselves against other sectors and to meet the changing expectations that customers have, including by offering more personalised and digital services. That is why from 2020, we are switching to a new measure (‘C-MeX’) of customer service, which will set an even higher bar.”