Here's the current splash screen on the ba.com site:
Welcome to ba.com
Following the major IT system failure experienced earlier today, with regret we have had to cancel all flights leaving from Heathrow and Gatwick for the rest of today, Saturday, May 27.
We are working hard to get our customers who were due to fly today onto the next available flights over the course of the rest of the weekend. Those unable to fly will be offered a full refund.
The system outage has also affected our call centres and our website but we will update customers as soon as we are able to.
Most long-haul flights due to land in London tomorrow (Sunday, May 28) are expected to arrive as normal, and we are working to restore our services from tomorrow, although some delays and disruption may continue into Sunday.
We will continue to provide information on ba.com, Twitter and through airport communication channels.
We will be updating the situation via the media regularly throughout the day.
We are extremely sorry for the inconvenience this is causing our customers during this busy holiday period.
If you would like to continue please click on one of the following links, otherwise please visit us again later
The links all seem to take you back to a version of this screen with some mixed language prompts.