Sainsburys are currently selling the Finish Quantumatic Dishwasher System Kit at half price £5.08. The website shows 'for deliveries until 24th May' so this must be the expiry date. These kits contain a cartridge for 12 washes.
Using the Finish £5 off voucher available from:http://www.finish.co.uk/quantumatic-coupon-5off.php
You can therefore pick these up in store for 8p each. My wife and I got one each last night with no problems.
That is a proper bargain at less than 1p a wash.
Apologies if this has already been posted but I searched and only found expired deals in other supermarkets.
*** JUST BEEN IN, YOU CAN GET THE LEMON ONE FOR £4.97 ***