A fleet of tilting trains is to be modified after toilets were found to be prone to overflows and blockages.
The problem was found on Virgin Trains' new Pendolino trains, used on the West Coast Mainline.
Alstom, the manufacturers of the state-of-the-art rolling stock, is now working to solve the problem.
Sir Richard Branson's £600m fleet will travel at 125mph, and reduce the journey time from London to the North West of England and Scotland.