Pinsent Masons has renewed its exclusive sole adviser relationship with energy company E.ON for another five years, after a competitive tender process.

The appointment, which will run until 2023, comes after Pinsents first won the exclusive mandate in 2013, since when it has acted as the energy company's sole external legal adviser, providing it with a range of legal services geared towards more day-to-day tasks.

Under the deal, Pinsents will support E.ON UK's in-house team, which includes head of legal Kirin Kalsi and senior legal counsel Rachel O'Reilly, on a pre-agreed fixed-price basis – a model the firm has lately implemented for clients including housebuilder Balfour Beatty.

Pinsents litigator Jonathan Fortnam, who oversees the relationship, said of the renewed tie-up: "By renewing our partnership, we can continue to provide valuable and strategic advice and support to E.ON UK. They play a vital role in the UK energy market and over the past five years we have developed an in-depth understanding of how best we can meet their needs. E.ON takes a long-term view of UK's energy sector, and we see this as the continuation of a strong relationship across the next five years."

Meanwhile, Kalsi added: "Our relationship with Pinsents has been an exciting and innovative arrangement and the success of this is evidenced by the latest extension to the agreement for another five years. The legal function at E.ON has a prominent role to play in ensuring our customers are treated fairly and that we act in an effective and efficient way to manage costs for our customers.

"Pinsents was able to secure the contract to continue providing legal services to us in the UK with a wide range of expertise, at a competitive price, with valuable added-value elements included and providing technical solutions to further enhance the way we provide legal services to our colleagues, which ultimately benefits our customers."

E.ON's UK arm supplies energy to about 4.3 million customers in Britain and employs more than 9,000 people across the country.

The wider E.ON corporation, which is headquartered in Germany, earlier this year sought advice from magic circle firms Freshfields Bruckhaus Deringer and longtime adviser Linklaters on a £38bn deal to acquire a controlling stake in renewable energy business Innogy.