Stumbled upon this whilst searching on ITA, cheaper than C on the same flights! AF F on the A380

London (LHR) to Miami (MIA) — Sun, Mar 13

London (LHR) to Paris (CDG) — Sun, Mar 13
Air France 1481
Dep: 8:20 am
Arr: 10:35 am
1h 15m
Airbus A319
Business (J)
Breakfast
Layover in CDG
3h 15m

Paris (CDG) to Miami (MIA) — Sun, Mar 13
Air France 90
Dep: 1:50 pm
Arr: 6:55 pm
10h 5m
Airbus A380
First (F)
Meal, Snack or Brunch
Miami (MIA) to London (LHR) — Fri, Mar 18
Overnight flight

Miami (MIA) to Paris (CDG) — Fri, Mar 18
Air France 99
Dep: 9:50 pm
Arr: 11:20 am
8h 30m
Airbus A380
First (F)
Meal, Snack or Brunch
Layover in CDG
Sat, Mar 19
2h 5m

Paris (CDG) to London (LHR) — Sat, Mar 19
Air France 1780
Dep: 1:25 pm
Arr: 1:45 pm
1h 20m
Airbus A320
Business (J)
Meal
Mileage
9,588 total miles
Airport Information
London Heathrow (LHR)
Miami International (MIA)
Paris Charles de Gaulle (CDG)
Cost per passenger (including taxes & fees)
£3,098.31
Total cost for 1 passenger
£3,098.31

Fare 1: Carrier AF F2SFGB LON to MIA (rules)
Passenger type ADT, round trip fare, booking code J, F
Covers LHR-CDG (Business), CDG-MIA (First)
£1,300.00
Fare 2: Carrier AF F2SFGB MIA to LON (rules)
Passenger type ADT, round trip fare, booking code F, J
Covers MIA-CDG (First), CDG-LHR (Business)
£1,300.

Not sure about other origins and destinations, but for those in LON, this is an amazing fare for F!