The exemption is also available where a property is owned by trustees and occupied by one of the beneficiaries as their main residence.
Until last December it was possible to transfer a property you owned but which was not eligible for CGT main residence relief into a trust for say the benefit of your adult children. Any gain could be deferred using the gift relief provisions. One of your children could then live in the property as their main residence and on sale the exemption would have covered the entire gain.
The Inland Revenue has decided that this technique was being used as a mechanism to avoid CGT and so has blocked the possibility of combining gift relief with the main residence exemption in these circumstances.