Sir Laurie said she did get legal advice when buying the property, but failed to seek further expert tax advice as recommended.

i know this was all gone over at the time but fuck me. the excuse for dodging stamp duty was that her house was held in a trust fund for her kid who was 17 at the time

five minutes or so on the gov.uk stamp duty website gets you:

https://www.gov.uk/guidance/stamp-duty-land-tax-buying-an-additional-residential-property

higher rates apply to [...] any residential property that [...] is owned on behalf of children under the age of 18 (parents are treated as the owners even if the property is held through a trust and they are not the trustees)

this counts as expert tax advice apparently