A fault with the signalling system between London and Stevenage means that trains have to run at a reduced speed on some lines. As a result, trains running between these stations may be delayed by up to 15 minutes.

Disruption is expected until 13:00.

Great Northern / Thameslink customer advice:

If you are travelling from Welwyn Garden City towards Hitchin you can travel on your normal route, but services will be disrupted.

You will need to allow at least an additional 15 minutes to complete your journey.

Please talk to station staff, look at the information boards or check your journey planner for the most recent information.

Can I use my ticket with another operator?

You can travel on the following services at no additional cost:

• Thameslink services between Welwyn Garden City and Hitchin
• Great Northern services between Welwyn Garden City and Hitchin

Please be aware that using alternative travel will add at least 20 minutes to your journey depending on the route.

Planning your journey with Thameslink:

For help planning your journey, check live departure boards, view a live network map or see alternative route guides.

Planning your journey with Great Northern:

For help planning your journey, check live departure boards, view a live network map or see alternative route guides.

If you’re travelling within London, you can use the TfL Journey Planner.

Stay up to date on the move with Thameslink's WhatsApp channel or Great Northern's WhatsApp channel. Live updates are available Monday to Friday, 07:00–21:00.

Can you tell me more about the incident?

There is a fault with the Train Protection and Warning System (TPWS), which is part of the signalling equipment. This is a safety system which monitors the speed of trains, and whether they have stopped correctly for red signals.

The TPWS system consists of electrical grids on the track which work with a sensor system underneath each train. In the case of speed restrictions, the system detects how long the train takes to pass between two fixed points. If this time is too short, it would mean the train has been travelling beyond the speed limit, and the grids will stop the train. For red signals, the grid adjacent to the signal will be switched on, and if a train passes the signal, it will also cause it to stop. These incidents are extremely rare, but every effort is taken to keep you safe during your journey.

In this case, the TPWS system is faulty, which means that other signals on approach to the fault will automatically be restricted, so drivers come to a stop before they get to the faulty equipment. Railway signalling works on "fail safe" principles. If there's a technical failure, the system should go into a more restrictive state, so that trains can be slowed or stopped in time.

However, this does mean that there will be some delays, as your trains can't travel as normal through the area. Network Rail are responsible for TPWS, as part of the signalling system, and they are attending as quickly as possible to resolve the problem.

Ticket flexibility:

If your train is cancelled, you will be able to travel on an alternative service operated by any other participating train company, either two hours before or two hours after the original departure time of the cancelled service, in order to reach your destination.

If you decide not to travel or cannot complete your journey due to cancellations, you are entitled to a full refund from your original point of sale.

For further information and guidance please contact your train company or speak to a member of railway staff.

Check before you travel:

You can check your journey using the National Rail 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.

A fault with the signalling system between Salisbury and Yeovil Junction means that all lines are blocked. As a result, trains are unable to run between these stations via Gillingham (Dorset) and will be revised or diverted via an alternative route.

Disruption is expected until 15:00.

Customer advice:

Engineers are currently investigating a loss of power to the signalling in the Gillingham area.

Long distance and mainline services

Services between London Waterloo and Exeter St Davids are expected to be delayed by up to 60 minutes, cancelled or diverted via Westbury and will not be calling at stations between Salisbury and Yeovil Junction via Gillingham. Journey times will take longer than normal.

How do I get to my destination?

You should allow extra time to complete your journey and continue to check station boards and the website for the latest service updates.

Your ticket can be used, at no extra cost, on Great Western Railway services between Salisbury and Westbury and between Westbury and Exeter stations.

Rail replacement buses have been arranged to operate a shuttle service between Salisbury and Yeovil Junction calling at Tisbury, Gillingham, Templecombe, Sherborne and Yeovil Junction. These are expected to be in place from 10:30 at Salisbury and from 11:00 at Yeovil Junction. These are not running to a timetable.

There will be a limited bus service to Tisbury station due to road height restrictions on larger buses in this area therefore, a few mini buses have been arranged to serve this station.

If you need any help with your journey, please speak to a member of staff or use a station help point.

If you would prefer to use local buses to continue your journey please check Traveline. South Western Railway tickets are not valid on local buses unless stated above.

Ticket flexibility:

If your train is cancelled, you will be able to travel on an alternative service operated by any other participating train company, either two hours before or two hours after the original departure time of the cancelled service, in order to reach your destination.

If you decide not to travel or cannot complete your journey due to cancellations, you are entitled to a full refund from your original point of sale.

For further information and guidance please contact your train company or speak to a member of railway staff.

Check before you travel:

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

For helpful advice if you need to travel on a rail replacement service, including accessibility and bicycle information, please use our Rail Replacement Services page.

You can find the pick-up and drop-off location of rail replacement services by checking station signage or by searching for your station on our Find a Station page.

Please be advised that replacement vehicles may be busier than usual, and you should allow extra time for your journey.

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.

Disruption caused by a fault on a train between London St Pancras International and London Blackfriars has now ended.