This works:-
Take 4 large, spring-fastening clothes pegs. Push the duvet into the top end of the duvet cover. Line up the top of the duvet along the seam and anchor it with the clothes pegs (1 at each corner and 2 spaced between), then just pull the cover down to the bottom of the duvet and fasten it. Remove the pegs before sleeping (or you'll get one up your nose).
