I don't know if you live not too far from Shepherd's Bush, but if you don't find any tix before the day, you can come in front of it... Sometimes, people sell tickets there... At the last concert, a girl paid the ticket the normal price : the person who sale it was supposed to come with a friend, but the friend din't show up i think... But she was LUCKY, most of the time, thay are more expansive...
GOOD GOOD LUCK