If the parties to a contract have incorporated an arbitration clause then the starting assumption is that they intend any dispute arising out of their relationship to be decided by arbitration. This is so unless the language makes it clear that certain questions were intended to be excluded from the arbitrator's jurisdiction. You can no longer argue fine verbal distinctions to exclude some disputes from the agreement to arbitrate. You will be taken to have agreed on a single tribunal for the resolution of all disputes unless you expressly provide otherwise in your contract.
Additionally, even if one party says that the main contract is invalid, and the other party disputes it, that dispute must still be decided under the arbitration clause. The invalidity or rescission of the main contract will not usually result in the agreement to arbitrate being invalid. The agreement to arbitrate must be treated as a distinct agreement. It is only voidable on grounds which relate directly to the agreement to arbitrate itself, for example in cases of alleged forgery of a signature of one party, or an agent acting without authority. Only in rare cases will the dispute negate the agreement to arbitrate.
[Fiona Trust & Holding Corporation & Ors v Yuri Provalov & Ors, reported in the House of Lords under the name of Premium Nafta Products Ltd & Ors v Fili Shipping Co Ltd & Ors (17.07.07)].