No idea, according to
@Plainsong he's received an invitation already. I haven't received anything yet ... I, too, have an online subscription ( for over 5 years ), have participated in multiple surveys etc ( last being a few days ago ) and have hundreds if not thousands of hours of playtime on my console. The unknown is how many consoles will the UK store receive ? If it's not many, then it's possible you may have to sleep, eat & breathe Nintendo daily to qualify for an invite. A lot of people are going to qualify for the bare minimum criteria on the website.