Strike Back wasn't a BBC show in the UK - it was commissioned by Sky and aired on Sky One. The first series aired a while back and is out on DVD/Blu-ray here.
(Sky is the main satellite pay-TV platform - though Sky One, their general entertainment channel is also available on cable for competition reasons. Sky One is a 'basic' channel - you have to subscribe to watch it, but it isn't a premium channel)
Not all British TV is made by the BBC - though a LOT of the original stuff is