I just saw this deal at Sainsbury's Luton.
At amazon 12 cartidges cost £41.90 and the Marella jug 9.99.
I hope that will be useful to someone
The Brita Marella Cool White Water Filter Jug is an environmentally friendly and economically useful option for households who want to help save the planet and yet have clean filtered water on tap. The top of the filter jug features a meter to remind you to replace the filter and the jug is dishwasher safe and fits in the fridge door. This deluxe pack includes 12 Maxtra cartridges which will keep you in fresh filtered water for a whole year.
The Brita filter system works by passing the water through a fine mesh filter. The ion exchange resin reduces lime scale, aluminium and heavy metals. Finally, active carbon filtration occurs which significantly reduces substances that affect smell and taste such as chlorine and organic impurities. The result: clean, fresh water from your tap.