s 40 Adjustment of contracts on changes in tax
40.—(1) Where, after the making of a contract for the supply of goods or services and before the goods or services are supplied, there is a change in the tax charged on the supply, then, unless express provision for the exclusion of any such change in the tax charged is contained in the contract or where the change in the tax has been taken into account, every such contract is modified as follows:(a) where the change in the tax renders that supply liable to be charged with tax or increases the amount of any tax charged or chargeable in relation to that supply, the supplier may add to the agreed price in the contract the amount of that tax or the increase in that tax; (b) where the change in the tax renders that supply exempt from tax or reduces the amount of any tax charged or chargeable in relation to that supply, the supplier may deduct from the agreed price in the contract the amount of that tax or the reduction of that tax. (2) References in this section to a change in the tax charged on a supply include references to a change to or from no tax being charged on the supply whether before or after 1 April 1994.