The airport operator said passenger traffic in April was down 22.7 per cent on the same month last year.
UK airspace was closed for six days in April because of the threat posed by the ash cloud from Iceland’s volcano.
The company’s cargo tonnage was up by 6.2 per cent despite the disruption.
And the cloud has continued to cause disruption to flights across Europe, with some Scottish airports the most recent to be closed in the UK.
BAA operates Heathrow, Stansted, Glasgow, Edinburgh, Aberdeen and Southampton airports in the UK. It sold Gatwick last year.