A power outage at a Colt datacentre brought down the main Lastminute website and subsidiary sites including Medhotels.com, Holidayautos.co.uk and Travelocity.co.uk. Lastminute's website was offline from 3pm on Friday 4 July until 2am the following morning, during a week that is traditionally one of the busiest of the year.
Colt said the fault was with the main circuit breakers for the data hall which hosted Lastminute.com's equipment.
"We have done a full root cause analysis and have put in place preventative measures to ensure it doesn't happen again at that specific data centre. We are also undertaking checks at all our data centres to avoid a similar incident at any of our facilities," said Colt.
"To put the power outage in context, it is very unusual in our experience - we have 18 data centres across Europe, thousands of customers and have been running highly resilient data centres for nine years."
Website downtime is expensive for companies such as Lastminute.com, which builds its entire business around a web presence, said Martin Couzins, managing editor of Travel Weekly,
He said the fact that the website was unavailable for so long at a traditionally busy time would have cost the company in both financial terms and in harm to its reputation.
"The whole business is based on looking for a holiday at the last minute and Friday is a peak time for people looking for to get away for the weekend, and is also a peak time of the year for people booking holidays," Couzins added. "It goes without saying that it is shocking that the site was down for 11 hours and I am sure it will not happen again."
Lastminute.com and Colt would not comment on whether back-up was in place.