Alistair bought a house on 1 April 2000 for £125,000 and occupied the entire house as his principal private residence until 1 November 2008. As from that date, he rented out two rooms (comprising one-third of the house) to tenants and retained the remainder of the house as his own residence. This arrangement continued until 1 October 2020 when he sold the house for £615,000. Compute the chargeable gain.