CG73950 - NRCG and the exemptions: Disposals from 6 April 2019: Indirect disposals: Calculating the gain
The gain or loss is calculated on the value of the asset being disposed of (for example, the shares in the company). This is under the normal rules for such disposals (see CG11800, and CG50200C), and no adjustment is made to reflect the assets that are not UK land. Similarly, if the person is disposing of the company in their capacity as a partner in a partnership, the usual rules for calculating that gain would apply.
The gain is calculated on the basis of the actual disposal and the rights that the disponer has at the time of the disposal. So in a situation where a person meets the substantial indirect interest condition (see CG73938) because they owned 25% or more of a company at a point in the two years prior to disposal, but now owns less than that e.g. if only 20% was owned at the time of disposal the gain would be calculated based on that 20% interest.