Answer ... The Arbitration Act applies only where the arbitration agreement is in writing (including an agreement made in writing (whether signed or unsigned), an agreement made by the exchange of communications in writing or an agreement evidenced in writing) (Section 5).
Arbitration agreements are typically set out in a clause within a larger commercial contract, but may also be set out in a separate document, incorporated into a contract by reference (Section 6(2)).
Oral arbitration agreements fall outside the scope of the Arbitration Act, but may also be recognised as valid under common law (Section 81(1)(b)).
Answer ... Under Section 7 of the Arbitration Act, unless otherwise agreed by the parties, an arbitration agreement which forms or was intended to form part of another agreement (whether in writing or not) shall not be regarded as invalid, non-existent or ineffective because that other agreement is invalid, did not come into existence or has become ineffective, and shall for that purpose be treated as a distinct agreement.
The leading English authority on the doctrine of separability is the House of Lords decision in Fiona Trust & Holding Corporation v Privalov  UKHL 40, which confirms that the effect of Section 7 is that the “arbitration agreement must be treated as a ‘distinct agreement’ and can be void or voidable only on grounds which relate directly to the arbitration agreement and not merely as a consequence of the invalidity of the main agreement”.
Answer ... The Arbitration Act contains no default provision on either of these elements. Where there is no agreement between the parties, the arbitral tribunal has the discretion to decide the language and the seat of the arbitration proceedings (Sections 3 and 34(2)(a) and (b)).