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What is even better is that these fares are available all the way through to September 2021 (with a gap during the Summer Holidays):
To see a wide range of dates quickly and easily, Google Flights is best. If you book direct with British Airways rather than an OTA, fares are a little higher (£1,195), but in the current situation, I would recommend paying the premium.
If you credited the flights to British Airways Executive Club, a member without elite status should earn just under 13,000 Avios and 280 Tier Points. Crediting to Alaska Mileage Plan might well be a more lucrative option though – you would earn about 21,000 (more valuable) miles.
There are some good fares to other parts of the Caribbean too, including Antigua for £1358, and Jamaica (with Virgin Atlantic) from £1,221.
I am personally comfortable booking flights for later on next year, though that could prove to be overly optimistic. Booking direct with British Airways should make any changes required relatively simple.
These are excellent fares, particularly for dates as far in the future as September 2021.
Hat tip: Luxury Flight Club