The cheapest domestic FlexFlight flight is flying Frankfurt am Main to Friedrichshafen, which is £96. This round-trip flight has 1 stop. For a one-way domestic FlexFlight flight, the cheapest route is Munich Franz Josef Strauss to Leipzig/Halle (1 stop) for £46.
The least expensive round-trip international FlexFlight flight is: -Ho Chi Minh City to Bangkok Suvarnabhumi, -0 stops, -£157 per ticket FlexFlight has international one-way flights available, but the cheapest is a flight from Ho Chi Minh City to Bangkok Suvarnabhumi for just £68. This flight has 0 stops.
No, there are no FlexFlight flights from London Heathrow. However, FlexFlight does fly from Antwerp Deurne on a weekly basis. You could also fly with TUI Fly Belgium from London Heathrow as an alternative travel solution.