Rail travellers across Britain faced disruption Friday after a fault in a radio system used by drivers and signallers nationwide prompted cancellations across the network. The issue, which occurred during the busy morning commute, has led to “short-notice” delays and cancellations throughout the UK, according to National Rail, which represents train operating companies. Lines affected include the Elizabeth Line serving London’s Heathrow Airport and the Gatwick Express to the capital’s second-biggest airport.

The fault mainly affects trains as they are preparing to leave the depot at the start of their journeys, but trains can run normally once they are underway, National Rail said. “This is because it is preventing our train drivers from contacting the respective signalling center this morning and a reset has to be performed before the train can start its journey,” South Western Railway reported.