Steve Robertson has stepped down as the chief executive of Thames Water with immediate effect.

Ian Marchant, who has been independent chair since January 2018, will become interim executive chair until a new CEO is appointed.

Thames Water said Robertson will remain an employee until 30 June to “ensure an orderly transition”, working with Marchant.

The company said the search process for his replacement is underway.

Utility Week understands the decision was mutual.

Both Robertson and the company “felt this was the right time” for new leadership to take on the operational and delivery challenges for the next regulatory period (2020-25).

Robertson, who was appointed CEO in September 2016, told Utility Week in an interview last year that he was in it for the long haul.

At the time he said he had no regrets taking on the role, although he admitted he was “perplexed” when he was first approached for the job at Thames Water.

In the interview with Utility Week, he said: “One of the things with infrastructure businesses is that you have to be very suspicious of people who come in, wave a big flag, have a short-term impact, and disappear again. It’s not that sort of business. How can I expect my teammates in Thames Water to be committed, how can I expect us to make long-term decisions, how can I expect my customers to trust me if they think I’m here to make a bit of a splash and then disappear?”

The company claims it has “successfully transformed” in a challenging environment and built strong foundations to deliver its strategy.

Marchant, interim executive chair, said: “On behalf of the board, I would like to thank Steve for his service as CEO and wish him all the best. He has done a great job leading the company through significant change, putting the building blocks in place for its long-term success.

“We need to continue to ensure that Thames Water is an organisation that both customers and staff feel proud of. We remain fully committed to our proposed business plan focused on providing industry-leading customer service through a substantial investment programme which we are determined to deliver.

“We look forward to working with our key stakeholders to make it happen. We play a vital role in the lives of millions of people and we are relied on to meet that responsibility each day. That is the challenge that the executive team, the board and I are all focused on.”

Robertson added: “It has been a privilege to lead an organisation that touches the lives of so many. I would like to thank all those I have worked with, both inside and outside the company, and am proud of what we have achieved over the last two and a half years. Of course challenges remain, but Thames is now on stronger footing and well positioned to deliver for its customers in the years to come. I wish everyone at Thames Water all the very best as I pursue new opportunities.”

Thames Water’s business plan for PR19 was placed in the significant scrutiny category when Ofwat published its initial assessment of the proposals put forward by water companies.

Robertson said he felt akin to a proud dad who had been told his baby was ugly.

Writing exclusively for Utility Week shortly after Ofwat gave its initial view of Thames Water’s business plan, Robertson said he was concerned about how the company could “significantly increase resilience” while spending less money.

Thames, along with the other companies in the significant scrutiny and slow track categories, resubmitted its plan to the regulator on 1 April.

It reduced its overall budget for the five-year period from £11.7 billion to £10.9 billion.

Ofwat will publish draft determinations for companies categorised as either slow track or significant scrutiny on 18 July.