Portsmouth to Waterloo trains skip Woking after Guildford from 10am to 6pm until Friday 14 August. Change at Guildford for Woking, with 38C possible Thursday.

If you catch a Portsmouth to London train through Guildford this week, check it before you leave. Between 10am and 6pm today, Thursday and Friday (12 to 14 August), South Western Railway is diverting some Portsmouth Harbour to London Waterloo via Guildford services away from their normal route through Woking, sending them via Cobham and Stoke d’Abernon after Guildford instead (South Western Railway).

The company says the diversion will not increase journey times. The catch is for anyone using those trains to reach Woking itself: diverted services do not go there, so SWR’s advice is to change at Guildford for a stopping service to Woking.

The cause is a set of points in the Woking area which, in SWR’s words, “at high rail temperatures can impact the normal operation of infrastructure and equipment”. Rather than risk a points failure on one of the busiest junctions on the network in the hottest part of the day, the operator is routing trains around it. The window opens at 10am, after the morning peak, but it does not close until 6pm, so afternoon and early evening returns from Waterloo are affected on all three days.

The diverted trains use the borough’s other route to London, the New Guildford line through Clandon, Horsley and Effingham Junction, which passes Cobham and Stoke d’Abernon and rejoins the main line near Surbiton. Normal Cobham line stopping services are separate from this and continue to run; our Guildford train times page explains how the two routes compare in ordinary weather.

Diagram of the diversion: from 10am to 6pm on 12, 13 and 14 August some Portsmouth Harbour to London Waterloo services run from Guildford via Cobham and Stoke d'Abernon instead of via Woking, with passengers for Woking changing at Guildford
Graphic by The Guildford Post.
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Thursday is the day to watch

The reason the railway is being this careful is Thursday. The Met Office issued an amber warning for extreme heat at 10:32am on Tuesday, running from 9am to midnight on Thursday 13 August, and Surrey is on the list of counties covered. Its forecast has temperatures “potentially reaching 37 or even 38 Celsius” in eastern, south eastern and Midlands areas (Met Office warnings).

The UK Health Security Agency has moved with it. The yellow heat-health alert we reported on Monday has been replaced by an amber alert for the South East, in force from midday on Tuesday 11 August until 9pm on Friday 14 August. Amber means significant impacts are likely across health and social care services, including a rise in deaths among people aged 65 and over and among those with health conditions (UKHSA weather-health alerts).

National Rail’s standing hot weather notice, updated on Tuesday evening, explains what the heat does to the railway: overhead lines expand and sag, line-side fires start more easily, and rails can buckle. Its advice for the rest of the week is to check before you travel, allow more time, and carry water; refill points are available at Network Rail managed stations (National Rail). Some operators have gone further than SWR: East Midlands Railway is advising customers to travel only if essential on Thursday, so anyone connecting to long-distance services beyond London should check that leg too.

What it means for you

  • Travelling to Waterloo from Guildford: your train may take the Cobham line instead of running through Woking between 10am and 6pm, but SWR says journey times are unchanged. Trains before 10am are timetabled over the normal route.
  • Travelling to Woking: do not board a diverted Portsmouth to Waterloo service. Change at Guildford for a stopping service to Woking, and allow a few extra minutes for the connection.
  • Thursday needs slack. With an amber extreme heat warning covering Surrey and up to 38C possible, further short-notice speed restrictions or alterations are possible across all operators. Check your specific train on the day rather than assuming Monday’s timetable, and see our roadworks and travel page for what is already planned on the roads.
  • If you are delayed, keep your ticket. National Rail’s advice is that you may be entitled to Delay Repay compensation from the operator.
  • The heat rules from earlier in the week still stand. Bins go out the night before for the 6am rounds, and the hosepipe ban remains in force; the detail is in Monday’s report.