In addition to being a gateway to/from London, a city with more airline seats than any other in the world, London Heathrow Airport is also the UK's main international hub.
According to OAG data for the week of 12-Oct-2019, London Heathrow Airport has direct links with nine UK regional airports (i.e. excluding London). It is feed from these nine airports that gives Heathrow its UK hub status.
However, there are 20 airports in other Western European countries that have direct flights to more UK regional airports than Heathrow has (week of 12-Oct-2019, source: OAG): seven of these have at least double Heathrow's regional UK links, led by Jersey, with 21.
The majority of these airports are southern European leisure destinations and they do not threaten Heathrow's hub status. However, three important European hubs have more UK regional links than Heathrow: Amsterdam (20), Dublin (18) and Paris CDG (14).
Amsterdam and Paris CDG both offer large global networks and each has more destinations than Heathrow in Africa and Latin America, while Dublin has a strong North American niche. In addition, although Madrid, Munich and Frankfurt have fewer UK regional links than Heathrow, these hubs each serve at least one UK airport with no direct Heathrow flights.