Rush hour trains were brought to a halt between Stevenage and Peterborough following a train fault and electrical problems.
Trains in both directions were stopped for around 15 minutes near Huntingdon at around 8.15am today (Thursday, April 7).
This was due to a suspected problem with the axles on an Edinburgh-bound train.
The lines reopened at around 8.25am, but a power supply problems caused additional disruption.
Passengers on all trains - including Thameslink, Great Northern, LNER and Grand Central services to London King's Cross - faced delays of around 20 minutes or more.
At around 8.25am today (Thursday, April 7), a Thameslink spokesperson said: "For about 15 minutes, services were at a stand in the Huntingdon area."
A National Rail spokesperson said: "The 7.30 London Kings Cross to Edinburgh service is delayed near Huntingdon due to an indication of a possible fault with one of the axles.
"Trains in the area were stopped while it is checked."
Trains are moving again.
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