There is something of the swings and roundabouts in this adaptation of the cracking BBC series. On the one hand, the feature length format allows us to develop more the Perry/Croft characters, on the other it removes some of the quickly-paced potency of the humour... Either way, though, it's still an hugely enjoyable watch that reconciles great sitcom writing from these two literal geniuses with a cast and scenario that delivers potent reminders of just how those "left on the shelf" determined to make a valuable contribution to the protection of their country against the Nazi scourge. It has…