Hi Michael,
If a property sale takes place "between two connected persons" there is a form that needs to be completed and sent in to HMRC. This is a form giving details of thr property, price it was sold for and if I remember correctly there is something on it regarding valuations whether this be an independent one from a surveyor or one can be carried out by the HMRC valuations team.
Details are on the HMRC site and I have a link for the forms but could not access the site for some reason today
http://www.hmrc.gov.uk/cgt/forms.htm
There should be some notes available to complete the form too.