Well that's just ******* great. Just got a email from Shell so I guess my switch to Sainsburys isn't going ahead. The Shell tariff is much more expensive, a extra 10p on each standing charge, almost a extra 3p per kwh on electricity and 0.6p per kwh extra on gas. With all the better of the poor deal gone this is going to be a very expensive winter!!
Can confirm I've had emails from both too.
I think my switch is a day ahead of @b0rn2sk8.