London's Heathrow: Europe's biggest airport
The sprawling facility west of London welcomed a record number of travellers last year, with the aviation sector having recovered from the turbulent Covid years.
Almost 84 million passengers passed through the airport in 2024 -- a third from the neighbouring European Union -- and up three million compared with the previous high in 2019, one year before the pandemic struck.
That compared with about 70 million accessing Paris Charles de Gaulle airport last year, nearly 67 million at Amsterdam's Schiphol and around 66 million entering Madrid's main hub.
Heathrow also experienced its busiest December on record last year, with more than seven million passengers, and expects a new yearly high in 2025.
Globally, Heathrow was the second busiest international airport behind Dubai last year, according to travel data firm OAG, which calculated its ranking by seat capacity.
Heathrow's closure would affect at least 1,351 flights to and from the airport, according to the Flightradar tracking site.
It said 120 flights to the airport were in the air when the closure was announced.
Third runway
The airport opened in 1946 as London Airport before being renamed Heath Row, a hamlet demolished two years earlier to make way for the construction.
Situated 25 kilometres (15 miles) west of central London, the present Heathrow serves 200 destinations in more than 80 countries, with passengers having access to four terminals.
Among its main flight destinations last year were Dublin, Los Angeles, Madrid and New York.
London has five airports serving the capital and towns nearby.
Capacity is stretched, especially at Heathrow whose two runways each measure almost four kilometres in length, while the airport covers a total area of 12.3 square kilometres.
The airport welcomed more than 31,000 flights per month in 2022, latest figures show.
Having axed thousands of workers during the pandemic, UK airports have struggled to recruit sufficient staff after the lifting of lockdowns, which when added to strike action, has caused delays to flights, baggage handling and passport processing in recent years.
Heathrow in December unveiled plans to invest £2.3 billion ($2.9 billion) over the next two years to upgrade the hub.
In January it won the backing of the UK government to build a third runway, with the government saying it would help grow the economy while respecting climate goals.
Building that new runway will cost far more than the announced upgrade and likely trigger fresh upheaval as environmentalists oppose its construction.
The airport's latest earnings show net profit rose nearly eight percent to £496 million in the first nine months of last year.