Slamfire,
No, the courts are not bound to support the decision reach by Sharia. If the party does not accept the decisionor believes they have reason to challenge, they can then take it to legal arbitration.
The whole point is Lord Phillips is confirming that:
A) British Law is the supreme law of the land
and
B) Citizens of Britain have the right to seek whatever arbitration in marriage, contracts, or other civil or financial disagreements outside the courts they choose. However the decisions/punishments/etc. of these arbiters must still abide by British Law. This isn't even a change TO the law, but the affirmation of the one already on the books (hence, why Orthodox Jews may ALREADY use the Beth Din for arbitration, in a similar manner to that which can be exercised by Muslims via Sharia)