Major rail services in London are facing severe disruption due to adverse weather conditions, leading to significant delays and cancellations. A 'do not travel' warning has been issued for several key rail lines, including Southern, Thameslink, and Gatwick Express. Passengers are strongly advised to avoid travel as services are severely impacted. The disruption is a direct result of the severe weather, which has affected rail operations across the city. Rail companies are working diligently to restore services as quickly as possible, but the situation is expected to persist throughout the day.