Restrictions put in place by the COVID-19 pandemic have delayed progress on the Thames Tideway supersewer project in London, England. The delays will also add an additional £233 million to the completion of the project, according to a shareholder announcement.

Project promoter Bazalgette Tunnel Limited, Thames Water’s development vehicle for the project, said that the project is now “likely to be completed in the first half of 2025” instead of the anticipated 2024 finish date.

New Civil Engineering reported that the investor report did warn of a scenario in which the COVID-19 impact could drive up the final cost to £4.1 billion. The report also outlined a second “worst-case” scenario that could see costs of the remaining work spiral by 24 percent, which translates to a total cost of £4.3 billion.

“For our plausible downside scenario, we modelled a 9 percent increase in the remaining costs to complete, taking the total to £4.1 billion. This is consistent with our most recent internal scenarios,” the report stated.

“We consider a severe downside case to be a 24 percent increase in the remaining costs to complete, which equates to a total cost of £4.3 billion. Both our plausible downside and severe downside cost increase cases include the estimated impact of COVID-19, making reasonable assumptions about the ability of the company to agree the most appropriate cost allocation with our stakeholders.”

The investor report also predicted a three-month delay resulting from the pandemic, which has now been tripled.

Tideway is reported to be in discussions with Ofwat on a package of measures that would mitigate the financial impact of COVID-19 on the company. Bazalgette Tunnel said that these discussions are ongoing but that an announcement on an agreement is expected this autumn.

Tideway confirmed that work on the majority of the project’s worksite resumed in May after a brief pause when the country went into lockdown to contain the pandemic. However, Tideway has said it is currently operating at a lower level of activity in order to comply with social distancing requirements.