On its webstite, Northern said: “High temperatures are forecast throughout the UK this week and may affect how our trains operate.
“To keep trains running reliably, we’ll be introducing a reduced timetable from Tuesday, 23 to Thursday, 25 June, and temporary speed restrictions are in place on some routes. We strongly recommend that customers check before they travel.
“Extreme heat can affect train performance and reliability, so we’re making these adjustments to help maintain a consistent service.
We will continue to monitor conditions closely and may make further changes.
“If you’re travelling this week, please check your full journey, including connections, before you travel.”