Several London rail services are cancelled as the UK heatwave pushes temperatures to around 34C, prompting disruption across parts of the network. One outlet reports that train companies are issuing warnings to customers and advising people to travel only if essential. The reporting focuses on the scale of cancellations and the expectation that further changes could occur as heat-related conditions affect rail operations. Affected services are listed by the companies responsible for running them, with cancellations differing by operator and route. The guidance to passengers reflects operational constraints during extreme temperatures, when equipment and track conditions can require reduced service levels.