The case in question involved a couple who inherited a second home from a deceased parent.
They complied with the usual filing deadlines and sent an election to have the second property considered as their principal private residence for the week before it was sold on 19 October 2007. If successful, the election would have had significant Capital Gains Tax consequences. For example if a property is at any time considered to be a principal private residence, the last three years of ownership will be ignored for CGT purposes.
HMRC rejected their claim.