Google has apologised for yesterday's major Gmail meltdown after some of its data centres in Europe failed to cope with a routine maintenance event. Businesses and individuals were unable to gain access to their email accounts via the internet until around 12:30 GMT on Tuesday. (See: Gmail failure sparks online panic)

''This morning, there was a routine maintenance event in one of our European data centers," said Google's site reliability boss Acacio Cruz yesterday. "This typically causes no disruption because accounts are simply served out of another data centre.

''Unexpected side effects of some new code that tries to keep data geographically close to its owner caused another data centre in Europe to become overloaded, and that caused cascading problems from one data center to another. It took us about an hour to get it all back under control.''

Google said it had fixed the bugs and also shared the pain with its users. ''We run Google on Gmail, so outages like this affect us the same way they affect you. We always investigate the root causes of rare outages like this one, so we can prevent similar problems in the future,'' said Cruz.

Many complained on the Google Apps and Gmail forums about the lengthy outage, while others worked around the problem by accessing their email using Imap on a desktop client or through their iPhone or other handset apps.

Premier Edition Google Apps customers such as The Guardian and Salesforce have been promised at least 99.9 per cent Gmail uptime per month. If Google fails to deliver on the terms of its service level agreement it has to cough up a penalty.

That translates as a commitment to no more than 45 minutes of downtime a month - so presumably, affected businesses will be expecting to see a refund. In fact it has been reported that Google is offering paying customers who cough up $50 per user, per year for the service, 15 days free credit.

The Guardian has said it will be ''demanding answers'' from the search firm over the loss of its online email service yesterday.

''Its less than ideal just before we start our pilot and we'll be obviously demanding some very detailed answers from Google,'' said Guardian Media Group director Andy Beale. ''We do have a service level agreement with them and I think they will have breached it this month with this outage.''