Blair moved Labour from the left to the Centre, a d Cameron has moved the Conservatives from the right to the centre. The result is that there isn't a great difference between the two. The Conservatives supported going into Afghanistan and Iraq, and most people know the financial crash was a global event, and only rabid Tories believe it was Brown's fault.
But the population is fed up with Labour and want a change. However, the Tories have only looked electable again for a short period, and people still remember them as the Nasty Party. Cameron has to convince the voters they have changed.