Antigua and Barbuda are two separate islands but, together, they make up one country.
If you're flying to Antigua, you'll land at V C Bird International Airport, at Coolidge.
Your departure airport will be determined by your choice of airline. Three of London's airports (Luton, Stansted and London City) have no direct flights to Antigua.
First Choice and BA operate from Gatwick (North)
Virgin Atlantic operate from Gatwick (South)
The only direct scheduled flights from Heathrow are with British West Indian Airways.
The only operator from Manchester is BMI.
Chris