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Friday 5 Jun 2026

Major upgrade to improve reliability for passengers under way on Thameslink route through central London

Region & Route:

Southern

| Southern: Sussex

• Back-up train detection system to prevent delays and keep trains moving in disruption
• UK’s largest third rail power substation replaced and train cameras fitted

Work has begun to upgrade a signalling system as part of major measures to improve reliability on one of the busiest parts of the rail network used by Thameslink, which this week transferred to public ownership.

As part of Network Rail’s ongoing investment to improve journeys and provide a dependable service for millions of customers across the UK, engineers are installing a back-up train detection system between London Blackfriars and Farringdon to prevent delays.  

Network Rail is also replacing the 20MW electrical substation between City Thameslink and Blackfriars station. This is the largest on the 750V third-rail network and is placed under heavy load with the volume of trains passing through.

And following a successful trial, Network Rail and Thameslink are also looking to fit thermal imaging cameras permanently to the front of Thameslink trains to detect ‘heat spots’ and catch faults before they even happen.

The Thameslink ‘core’ route between London St Pancras International and Blackfriars is one of the most intensively used sections of railway in the UK, with up to 44 trains per hour on a two-track system connecting services from Kent, Sussex and the East Midlands through the heart of London.  

With frequent trains and no diversionary routes available, even small faults can quickly cause disruption across the network, as far afield as Brighton and Cambridge or Horsham and Peterborough. 

Work has already begun on the signalling upgrade, with two more weekend track closures planned for June carefully planned to reduce overall disruption while allowing engineers the time they need to complete the upgrades safely. 

Louise Greaves, Network Rail’s Infrastructure Director said: “The heart of Thameslink, in central London, is one of the most critical sections of railway in the country, where even small issues can quickly have a big impact on thousands of passengers. 

“By installing a dual detection system, upgrading the power supply and looking at the fitment of train cameras, we’re making a targeted investment in reliability and resilience. Two detection systems means that even if one fails, trains can keep moving, reducing disruption and improving journeys for passengers.” 

Jenny Saunders, Thameslink’s Customer Service Director, said: “These upgrades are a really important step towards reducing delays and giving customers a more consistent, dependable service in the future. We know how important reliable journeys through central London are.

“We’re sorry to customers who may be affected while this work takes place, and we’ll be working closely with Network Rail to keep people moving and provide clear, up-to-date travel information. I’d strongly encourage anyone planning to travel over these weekends to check their journey before they travel.”

'Dual detection' technology has already been introduced successfully north of Farringdon in 2020, where delays caused by track circuit failures have declined. Similar improvements are expected once the new system is in place between Blackfriars and Farringdon. 

Following installation, the system will be tested over the autumn of 2026, with final commissioning planned by the end of the year.