I think it was correct to send Swann in at 6, but a few sighters wouldn't have gone a miss. Swann is capable for whacking the ball and a quick 20-30 would've pushed the game away from the Lankans.
Just look at Sanga's body language at the end of England's innings, rather concerned look on his face.
Final point, Murali looks a shadow of his old self. He bowled very poorly today. When do you ever see Murali going at a run a ball in Coloumbo?