The biggest stakeholder in supermarket group Sainsbury has sold shares in the group, making this the second occasion in seven days.

Judith Portrait, the trustee of several trusts set up by the Sainsbury family, sold a million shares in the supermarket group for about £3m, accounting for 0.05% of Sainsbury stock.

The shares are understood to have been owned by four charity trusts as well as family members.

Last week the Gatsby Charitable Foundation, a Sainsbury family charity of which Ms Portrait is also a trustee, sold a 2.6% stake in the company for £130m.

The two sales have reduced Ms Portrait’s stake from 23% a few weeks ago to 20.96% yesterday.