Tideway Chair Sir Neville Sims has described the delivery model for the Tideway Tunnel supersewer as an “exemplar for securing long term private capital to provide large scale UK infrastructure alongside our approach to achieving significant wider social value.”

Tideway is the privately financed company responsible for building, commissioning, financing and maintaining the Thames Tideway Tunnel.

To date shareholders have invested £1.3 billion, with close to half the total equity coming from UK investors, including many pension funds, giving 2.7 million UK pension holders a stake in Tideway.

Commenting in Tideway’s Annual Report and Accounts published at the end of Augustt, Sir Neville said Tideway’s shareholders were continuing to provide valuable support, saying:

“As we move closer to completion, we can be increasingly confident about the final phase of delivery. In September 2022, when DIF Capital Partners divested its stake in Tideway following one of its underlying investment funds reaching the end of its fund life, our other existing shareholders acquired DIF’s shares, confirming their commitment to the company…..

“At a time of unprecedented concern for the protection of waterways we are offering a positive solution – we are the UK’s largest intervention underway to tackle sewage pollution and the benefits of the project are now just around the corner.

“Tideway is the third stage in a decades-long and ongoing endeavour to tackle sewage overflows in the London region. The first two stages (the Lee Tunnel and sewage treatment work upgrades) were delivered by Thames Water and this year we saw a glimpse of the impact and outcomes of this investment.”

The construction programme for the Tunnel is almost 90 per cent complete and Tidway is now focussing on preparations for system commissioning which will start in 2024, ahead of full operation in 2025.

The company has increased its engagement in some areas to reflect the pace of the project in the closing stages. Since the start of 2023 its Liaison Committee (with government and regulatory stakeholders) meets monthly and the Thames Tideway Tunnel Forum (with consenting bodies and delivery partners) meets once every two months.

Tunnel System Commissioning phase of the project due to start in 2024

The company is now moving into the System Commissioning phase of the project which is due to start in 2024.

After testing of the mechanical and electrical equipment at the worksites by the three Main Works Contractors (MWCs) , the System Integrator Contractor will complete the connection of these sites to the overall London Tideway Tunnels (LTT) control system.

All the elements of this system will then undergo extensive testing in the dry before any sewage flows are received. Once this is complete, the final physical isolation will be removed between the existing Lee Tunnel and the new Thames Tideway Tunnel. The Combined Sewer Overflows (CSOs) along the Tideway starting with the Abbey Mills CSO will also be activated to the new LTT system.

Once these are all activated a series of storm tests will be carried out in a gradually incremental manner over several weeks culminating in a 30-day period of automated operation. After this final test the tunnel will be inspected, and the operation of the system handed over to Thames Water.

Handover will then be followed by the System Acceptance Period - a proving period of between 18 and 36 months in which the LTT will be operated across a variety of climatic conditions to demonstrate that it fulfils the project requirements.

Once this is complete, Thames Water will become responsible for maintaining the near-ground structures and assets with Tideway retaining responsibility for the shafts and tunnel structures and ensure the TTT is available to allow flow to pass to the Lee Tunnel.

Tideway expects to inspect the deep tunnels and shafts on a ten-yearly cycle and will carry out any maintenance as required.

Tideway "remains confident that "impact on customer bills will remain well within estimate of £20-25"

The cost estimate for the Tunnel is currently £4.5 billion which is a five per cent increase from the previous year (two per cent since the interim accounts), with the cost of prolongation and cost inflation being the most significant contributors to change.

According to Tideway, while uncertainties remain, which it describes as “typical for projects at this stage that could impact on future costs”, it remains confident that “the impact on customer bills will remain well within the pre-Licence award estimate of £20-25 (in 2014/15 prices).” Tideway says it is also on track to stay within its original carbon footprint target of CAPEX (embedded) (Scope 3) ~770,000tCO2e.

Each of the MWCs’ target prices have been adjusted to reflect Compensation Events (risks retained by Tideway). The primary areas of change to the MWCs relates to finalisation of the programme to contractual completion and the introduction of Tideway’s Phased Commissioning Plan to the MWCs’ scope of work.

Click here to download Tideway's Annual Report & Accounts 2022/23