The latest figures are still less than the six million people that passed through in January 2020, but Heathrow boss John Holland-Kaye said the airport was back to its best. Some 17,458 flights are scheduled to depart UK airports during half term, but overall departures remain 19% down compared to the same period in 2019.
Cirium said departures were up 43% on last year's February break. The air travel industry was grounded during the peak of the Pandemic, and was able to recover, it said.
Heathrow said passenger satisfaction was at or above pre-pandemic levels, with 98% of passengers waiting less than 10 minutes for security last month, which is typically a quieter time of year for UK passengers.
The airport said that Border Force was trialling using e-gates for children aged 10 and 11 in Terminal 5 over the half-term holiday, as it was also doing in Gatwick and Stansted.
There have been thousands of workers calling for pay rises in order to keep pace with the rising cost of living in recent months. The rate at which prices are rising in the UK is currently at 10.5%.
A spokeswoman for Heathrow said the airport was extremely disappointed by Unite's move and warned that if the strike begins, the pay offer will be withdrawn. It said its 10% salary increase offer came at a time when the business was making losses.
In December Border Force staff went on strike for several days, but Heathrow said that the Border Force had drafted in military personnel and civil servants to cover around 1,000 staff, many of whom are responsible for checking passports, and delays to travels were reported to be minimal.
Thousands of passengers faced delays and flight cancellations across the UK last year, with airports and airlines struggling to recruit enough staff to cope with the surge in demand for international travel after the removal of Covid restrictions.