A train operator is running services lasting more than five-and-a-half hours despite having no toilets available on board.
The Lumo trains run on the West Coast Main Line, covering the new 417-mile (671km) route between
Stirling and London Euston.
Lumo, which is owned by FirstGroup, first warned about a "fault" with the toilets on a service from Stirling to Crewe on Saturday.
Some services have since been stopping for longer at stations such as Preston to allow passengers to get off and use toilets on platforms.
A Lumo spokesperson said: "We have been experiencing some issues with the reliability of some of our toilet facilities onboard our West Coast services."
They added that they were working closely with rail company Alstom, which refurbished the carriages used by Lumo, to "rectify the issue".
The 06:11 departure from London Euston on Friday, which was affected, ran with a 58-minute delay and terminated at Motherwell, North Lanarkshire.
Passengers were told their tickets would be accepted on ScotRail services.
Liberal Democrat transport spokesperson Olly Glover posted on social media: "Is Lumo attempting to become the Ryanair of the rails?"
Train operators in Britain are not legally required to provide onboard toilets.
Lumo operates its West Coast services with refurbished Class 222 Meridian trains.
These are also used by East Midlands Railway, which has also suffered toilet faults with its fleet.
Lumo also runs services on the East Coast Main Line, connecting London King's Cross with Edinburgh, Glasgow and Falkirk.
It operates on an open access basis, meaning it sets its own fares, takes on all revenue risk and receives no taxpayer-funded subsidies.
It is not affected by the government's renationalisation of all remaining franchised train services in Britain.
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