Seen on another site

A heads up not to spend nectar points in Sainsbury's before 10 April because they are doubling the value of them from the 10th to the 30th April instore.
Double the value of your points at your nearest Sainsbury's supermarket. Selected categories only.
Probably be like Tesco double points event, but this is the first time Sainsbury's and Nectar will be doing it.
Full terms and conditions but the web page is not yet live