Samantha Cameron's Shareholding

The Telegraph reports:
"Samantha Cameron has a shareholding in the firm aiming to construct up to 1,000 homes in rural Lincolnshire."

Apparently Mr Cameron and the Cabinet Secretary Sir Jeremy Heywood agreed that the shareholding was not a “relevant interest” to be included in the ministerial list of interests. Strangely, her roles as patron for three charities and with the British Fashion Council were considered  "relevant".

One would have thought this shareholding was highly relevant with the government's emphasis on boosting the construction industry and easing planning restrictions. I wonder how many other members of the government (or their wives) have such interests which are not considered "relevant".