Agreements in writing of market value or apportionment
12.—(1) An agreement or notification which apart from this Regulation would have effect under section 510 of the Income Tax Act 1952 (settlement of appeals by agreement or withdrawal) as if an appeal had been determined by Commissioners shall not have that effect in relation to any appeal in which a third party has been joined unless, at the time when such agreement is made or notification is given, the question in which the third party is interested has been finally determined on the appeal or disposed of by an agreement made in accordance with paragraph (2) below.
(2) Where the market value of an asset on a particular date or the apportionment of any amount or value may affect the liability to capital gains tax of two or more persons and is a material question in an appeal, then if the market value or apportionment is agreed in writing between the inspector or any other officer of the Board and all the parties to the appeal whose liability may be affected by it the agreement shall in all proceedings relating to capital gains tax be conclusive between the Board or any officer of the Board and the following persons—
(a)parties to the agreement; and
(b)any person who was entitled, in respect of the question in the appeal to which the agreement relates, to apply to be joined as a third party in the appeal, and had notice of the appeal and of the question in the appeal not less than thirty days before the agreement was made, not being a person who did so apply before the agreement was made.
(3) A document purporting to be an agreement made in accordance with paragraph (2) above and produced from proper custody may be received in evidence in any proceedings relating to capital gains tax without further proof as such an agreement made by the persons by whom it purports to be signed.