Trains between Norwich and London are being delayed and cancelled because the hot weather means a speed restriction has been put in place.
The 5pm service from London Liverpool Street to Norwich has been cancelled due to the issue, as was the 2.30pm Norwich to London Liverpool Street service.
The 1pm and 3pm services from the capital to Norwich were delayed because of the restrictions.
Rails in the UK are stressed to 27 degrees, the UK mean summer rail temperature.
The rail can withstand some degree of change in temperature either side of this. But when they get particularly hot, they expand and this can cause a type of signalling problem called a track circuit failure and in extreme cases can cause a buckled rail.
If a rail buckles then the train service will not be able to run at all until the buckled rail is replaced with a new one.
When Network Rail assesses that the temperature of the rails is going to exceed what it is designed to cope with they put speed restrictions in place to help prevent buckled rails.
Details on services affected are available here:
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