My girfriend works at Sainsburys head office and just sent me this info
From tomorrow we are running a seven day market leading Only £10 promotion on 4175636 Etienne Dumont Champagne . This line is currently on a half price deal (£27.99-£13.99) on Grocery plinth 2, and the offer will be up-weighted to Only £10 from tomorrow. The deal is supported by national press. Additional stocks have been allocated to support the stunt.