Firstly, do Nike have much store front presence in the UK, other than factory / outlet stores? I can't recall having seen them on high streets in Aberdeen / Edinburgh / Glasgow, since they're typically just stocked along with Adidas / Reebok as part of general sports stores (i.e. JD / Sports Direct).
Either way, personally, I can't see it. There may be some token replicas around Wembley in the build up to the International Series, but my perception is that the Brits just don't have the same fascination with jerseys that our American counterparts do (ok, maybe aside from the member on this site!) I think a big part of this is because the price point for a football (soccer) shirt in the UK has always been about GBP 40 (so around $60). Compare that to entry level replicas in the NFL and you're taking more like GBP 60. I can't see the average fan with a semi-interest in the NFL dropping that on a replica. By the time you've factored in shipping to the UK (and I've heard murmurings of Nike hiking prices), I actually think the replicas would be more like GBP 70 - so pushing on twice the price of a soccer shirt.
It's also been well publicised that Nike are cutting the "little guy" out, and only distributing through major retailers - at least initially. So unless Nike perceive there to be a major opening in the UK market for NFL jerseys, I don't think they'll bother. Who knows - you may start to see them within a few years, if the International Series continues to gain momentum and interest increases.