Staff at London Ambulance Service NHS Trust recorded emergency calls on paper on Christmas Day when its call management system went down for five hours.
A trust spokesperson said an issue meant a key database was not working between 4.30pm – 9.30pm.
The trust experienced problems again on Boxing Day, when an electrical fault affected the system for around three hours.
The trust uses the CommandPoint call handling software and an Oracle database.
“We did experience some technical problems with our call management system over the Christmas period,” the spokesperson told EHI.
"As a result, we reverted to our manual process of recording calls on paper and passing information to ambulance crews over the radio while the issues were resolved.
"During this time, calls continued to be answered, with priority still being given to those people with more serious illness or injuries.
"The technical issues, combined with high demand, meant that some patients had to wait longer than normal for a response from us."
The spokesperson confirmed that the system is now working normally and it will look in detail at what happened to see if there are any lessons that can be learnt from the incident.