Try checking through here:
http://www.hmrc.gov.uk/sdlt/intro/basics.htm
http://www.hmrc.gov.uk/sdlt/reliefs-exemptions/no-sdlt-return.htm
Specifically, this seems to cover what you are intending....
Property transactions where no money or other consideration changes hands
Property or land may be given away or the ownership transferred to another person for no 'chargeable consideration'. This means that no money changes hands, and there is no other exchange which has a monetary value, such as a mortgage debt. This type of property transaction is exempt from SDLT and HMRC doesn't need to be notified.
However, I'd run this past HMRC to clarify their take on it.