You don't 'sow' strawberries you buy plants unless you know someone who has strawberry plants and is willing to give you runners. End of June to end of August is when you plant them, for more info go to
http://www.bbc.co.uk/gardening/basics/techniques/growfruitandveg_strawberries1.shtml

Fraises du Bois grow from seed, but I have no idea how to grow them in the UK.

Your right Tugbrethil and it is a happily invasive wee plant in our garden but how we came by it in the first place I have no idea! Tiny berries incredibly sweet. Thompson and Morgan have them
http://www.thompson-morgan.com/seeds1/product/724/1.html
With full growing instructions. Or you can buy the plants of same.