Unit 2 Market failure; the London congestion charge

From tutor2u comes this update on Ken Livingstones latest plan to charge 4x4 drivers a higher congestion charge

http://www.tutor2u.net/blog/index.php/economics/the-london-pollution-charge/#When:21:29:00Z

a) In what way will this alteration to the charging system internalise the externality and make the polluter pay?
b) Suggest reasons why this system may not really internalise the externality