Earlier in the day, the UK's flagship carrier said all flights from the Heathrow and Gatwick aiports had been cancelled up to 5pm local time, but a spokesman later told AFP that all flights for Saturday had been grounded.
Angry passengers were forced to return home or to hotels, as the airports were emptied of people booked on British Airways flights, including those to the Middle East.
Suspicion at first fell on hackers, but the British airline said it is yet to see proof of this.
British Airways asked customers due on other flights not to come to the London airports, after a global IT problem disrupted flights worldwide.
The disruption came on a particularly busy day for Heathrow and Gatwick when families often holidays abroad for schools' half-term break.
Agencies contributed to this article.
Chaos in London airports as BA ground flights
Chaos in London airports as BA ground flights
MENA
1 min read
London airports are in chaos after an IT problem caused British Airways to ground all flights in the UK capital, leaving passengers to the Middle East stranded.
London airports are in chaos after an IT outage forced British Airways to ground all flights out of the UK capital