Passengers travelling between Stevenage and London can expect their journey to be extended by at least an hour, and are advised to consider taking alternative routes, due to a signalling system fault in Welwyn Garden City.

The fault is causing major disruption, with services cancelled, delayed or revised - which is expected to continue until at least 11am.

Trains will be diverted via Hertford North where possible.

Great Northern has posted the following advice:

LNER customer advice:

Customers may also use the following services to help with journeys:

East Midlands Railway between Sheffield and London St Pancras International

Northern between Doncaster and Sheffield

CrossCountry between Leeds and Sheffield

Great Northern/Thameslink customer advice:

There will be major disruption with cancellations to:

All trains to and from London Kings Cross

All trains to and from Moorgate

All trains from Peterborough and Cambridge through to London St Pancras International.

Leave as much time for your journey as you can, or consider either travelling later today or using an alternative route.

If you travel now, your journey is likely to be extended by at least one hour.

Where possible, trains will be diverted through Hertford North, but this will also extend journeys.

Your Great Northern or Thameslink tickets will be accepted at no extra cost on:

- London Overground between Enfield Town and Liverpool Street

- Greater Anglia

- Between Cambridge and Ely

- Between Cambridge and London

- Between Hertford East and London Liverpool Street

- Thameslink between Bedford, London St Pancras and Farringdon (these services may also be disrupted due to a signalling problem in the Farringdon area

- CrossCountry between Cambridge, Ely and Peterborough

- East Midlands Railway between Peterborough and Ely

- Tube services on any reasonable route across London

- Metroline buses on routes 84 and 242