Ed,
Perpetual strawberries often have a strong flavour.
To boost their flavour you could increase the amount of light coming to
the plant by placing a reflective mulch under the plants. Ken Muir
sells a woven membrane that is foil coated which is said to improve
sweetness. In glass houses, a white polythene is used for tomatoes for
a similar effect.
Clifford
Bawtry, Doncaster, S Yorks