I stay well, well clear of anything like this. To qualify for any prize (and your chances of winning anything at all are minuscule) you have to supply address/phone/email details. Morrisons then sells lists of these to marketing companies who will then target you with unsolicited phone calls and spam emails.
Whenever you see something which offers you the chance to win prizes and 'all you have to do' is fill out a contact form, my advice is to bin it.