A fault with the signalling system at Three Bridges means some lines are blocked. As a result, services may be delayed or revised.

Disruption is expected until 13:30.

Customer advice:

A signalling problem is delaying some Southern and Thameslink services via Three Bridges.

This issue is mainly affecting the following routes:

• Southern services between London Victoria and Portsmouth Harbour / Bognor Regis
• Thameslink services between Peterborough and Horsham
• Thameslink services between Bedford and Three Bridges via Redhill

We don't have an exact estimate for any delays at the moment, but please leave at least 20 minutes of extra time.

There will be some train alterations and cancellations at short notice.

You'll be able to see any further updates on this page, so please continue to check back here.

If you're waiting on a train which is delayed between stations:

If your train is delayed between stations, please remain where you are and listen to announcements, or speak to staff for further information. We'll get you moving as soon as possible. We're aware of your location, and our teams will be doing everything they can to help you continue your journey.

Please don't leave the train unless you are asked to do so. Other trains may still be moving in the area, and the track is also a very hazardous environment. In areas where the trains are powered by an electric third rail, this usually stays live and dangerous during incidents, and looks the same as other rails.

Alternative journey options:

Your ticket will be accepted at no extra cost on:

• Metrobus services on any reasonable route between Redhill, Gatwick Airport, Three Bridges/Crawley and Horsham
• Alternative Southern and Thameslink services on any reasonable route, including Southern services between Horsham and London Victoria via Dorking
• Great Western Railway services between Dorking West / Dorking Deepdene, Redhill and Gatwick Airport
• South Western Railway services between London Waterloo, Havant and Portsmouth Harbour

Planning your journey:

Live departure boards can be found here.

You can view a live map of the network here.

You can also see an alternative route guide here.

Can you tell me more about the incident?

A signalling fault known as "route locking" is causing disruption to your journey in this area. At the moment, we're working with local staff and our colleagues at Network Rail to assess the situation.

This part of the network uses track circuits to detect the position of trains. These are electrical systems which monitor whether a train is on a section of track. Track circuits operate as part of the signalling system, which is designed to be "fail safe".

When a track circuit fails, the signalling system will interpret this as a train remaining in place, even though there may not be a train present at all, or the previous service may have long since left the area.

In the case of track circuits at junctions, this means the points cannot be moved, as there could still be a train present. As a result, the junction will become route locked. The junction will then only be able to be used for trains running on the route which was selected when the system failed.

Until the track circuit clears, it won't be possible for your train to pass the area as usual, and if the route is locked, it may mean your train cannot reach its normal destination. Because this type of fault can result in a queue of trains waiting to continue, even if your own route is open, there can still be disruption to your journey .

Network Rail staff will be attending as quickly as possible to resolve the fault and make sure all of the affected trains can move. We're closely monitoring progress updates. Thank you for bearing with us. We're very sorry for the disruption to your journey today.

Check before you travel:

You can check your journey using the National Rail Enquiries real-time Journey Planner.

Compensation:

You may be entitled to compensation if you experience a delay in completing your journey today. Please keep your train ticket and make a note of your journey, as both will be required to support any claim.