Just an update regarding this offer from M&S listed on this site around February 2011. The offer was obviously a misprice but for those that ordered one I'm guessing M&S will have recently delivered your Xbox (but without the Kinect).
They will try to get out of sending the Kinect due to the misprice error but I found they buckled within about 10 minutes and agreed to send it. They are picking it up tomorrow and redelivering an Xbox with the Kinect at no extra charge. Make sure you get a confirmation email that they are doing this before the Xbox is picked up otherwise they may just refund you instead.