Depends on what you call CAS. Dropping precision weapons very close to your own troops from on high (through cloud, at night, as required) is CAS. Strafing the enemy very close to your own troops (CRV7 rockets or gun) is CAS. Flying very low over the enemy to scare them off is CAS.
Throw in a bit of photo recce/NTISR from Raptor, DJRP, Litening 3, Sniper to see what is ahead of your own troops, can be counted as CAS.
Tornado and Harrier can both do the above. The question is: is it worth the expense to make sure that Tornado can do everything in the future that Harrier is doing at the moment? Will the handover lead to a capability gap in the sky over Helmand? (I sincerely hope not - hence the delay whilst more Tornado are made PW4 capable).
Discuss ad nauseum.