Home exchangers can have problems finding a policy which includes adequate cover for cancellation.
Most travel policies do not cater for home exchangers, who are dependent on the other party vacating their home before they can move in. There is a company which recognises the need for this type of cover and who will offer cancellation cover if your exchange partner cancels for an insurable reason. They are GJ Sladdin and can be contacted on 01422-339152 - just quote HomeLink and they will explain their cancellation policy. Obviously you will need to check the small print of the policy document to ensure that the cover meets your needs.