North Herts commuters can expect long delays in the hot weather this evening after fire alarms at the London King’s Cross signal box stopped all services for about 45 minutes.

The signal box, which was evacuated at about 4pm, controls all of Great Northern’s route and signals up to Peterborough and Cambridge – meaning all services were affected until staff were cleared to return by the emergency services shortly before 4.50pm.

There is little indication on when services will return to normal, with Great Northern offering an estimate of disruption until ‘at least 8pm’.

Train service controllers, who would have co-ordinated replacement buses, were among those evacuated after the fire alarms went off.

Commuters have taken to Twitter to pass comment, with some stressing the hot weather.

Lucas Hare wrote: “All @GNRailUK trains delayed by around 40 minutes. It reminds me of that time when it was so hot that the track was in danger of buckling.”

A Letchworth user identified only as ‘Greg’ agreed: “Credit on getting the Royston train moving so quickly, shame it’s hotter than a furnace.”

Services on the Great Northern line are now running again. For live updates see thameslinkrailway.com/your-journey/tl-test.

Anyone delayed by more than 30 minutes on Great Northern services can claim compensation at greatnorthernrail.com/delayrepay.