Heathrow said passenger numbers hit 5.95m during the month, an increase of 3.4 per cent on the same period last year, making last month its busiest ever March.
It put the increase down to "larger, fuller, quieter aircraft" - the number of seats per aircraft increased 1.6 per cent to 206.4, while load factor (how full the aircraft were), increased to 73.3 per cent, and passengers per aircraft rose 3.2 per cent to 151.3.
The airport added that Mexico had become particularly popular - passenger volumes rose 26.5 per cent, while the number of travellers to China increased 20.2 per cent and Middle East and central Asia rose 7.6 per cent.
Gatwick, meanwhile, said it had experienced "record beaking" traffic figures, with 2.96m passengers, pushing the total up to 38.7m between April last year and March this year - a 7.8 per cent increase on the same period last year.
Its biggest growth area? Dubai: the number of passengers heading there increased 14.7 per cent, although the number of scheduled services heading to European destinations increased 12.1 per cent, with Barcelona the biggest "growth" destination, while Geneva was the most popular destination across its entire network (thank you, ski bunnies).
The figures make the decision by Sir Howard Davies' Airports Commission, which is due publish its findings on whether to expand Gatwick or Heathrow in May, even tougher. Davies, who, after several years of chairing the commission, would presumably like to get on with his new role as chairman of RBS, has already put off publishing the results of his politically sensitive findings until after the General Election.
Still, the chief executives of the two airports seemed keen to have the last word.
War of words - the chief executives make their cases