The Chancellor announced in his Budget statement that he intends to bring gains made by non-UK residents from the disposal of UK commercial property within the UK tax net. Historically, non-UK residents have not been liable for UK tax on gains made from the disposal of UK property (save where, exceptionally, the non-resident carried on a trade in the UK through a UK permanent establishment and the property was used in that trade).
As a consequence of this announcement in the Autumn Budget 2017, gains made by non-UK residents from the disposal of all UK property (both residential and commercial) after April 2019 are potentially liable to UK tax at the rate that would apply to an equivalent disposal by a UK resident. For non commercial properties gains made by non-UK residents after 5th April 2015 are liable and it is therefore beneficial to get a market value of the property as at 5th April 2015 for residential properties and to ensure that a market value is established as at 5th April 2019 for commercial properties.
It is important to note that where the disposal relates to a UK commercial property that was acquired before April 2019, it is only the gain attributable to the period from April 2019 that is liable to UK tax. Any gains attributable to the increase in value until April 2019 will not be liable to UK tax.