You should pay CGT on:
The sale or gift of the whole or part of an asset.
For example out of a 10 acre plot of freehold land, 5 acres is sold.
Capital gains tax will be paid on the disposal of the 5 acre part.
The loss or destruction of an asset.
For example a painting costing £5,000 was destroyed in a fire.
This destruction will be considered to be a capital disposal.
The disposal proceeds will be Nil and therefore a capital loss of (£5,000) will be realised on destruction.
Compensation in connection with an asset.
For example a painting costing £5,000 was destroyed completely in a fire.
The painting was insured and insurance proceeds of £10,000 were received because of the loss of the painting.
Capital gains tax should be paid on (£10,000-£5,000) = £5,000.
All assets are chargeable unless specifically exempted.
This list is provided in Topic: Assets which are exempt.
An individual who is resident in the UK is a chargeable person and is therefore subject to UK CGT on their worldwide assets.
Note the differences between companies and individuals
Companies pay corporation tax on their capital gains whereas individuals pay capital gains tax.
Companies have an indexation allowance up to December 2017 which allows for the adjustment of the cost of an asset for inflation, whereas individuals have an annual exemption.
Companies can use rollover and holdover relief with respect to their chargeable gains whereas individuals have a much wider array of reliefs available to them.
Companies can be part of 75% gains groups whereas individuals cannot.
Loss relief is dealt with differently between both companies and individuals.