Know that you posted the query ages ago, so you've either found it yourself or given up by now!
Blue Moon is now available off-trade (trial) in Sainsbury's, and on-trade (trial) in some of the higher-end M&B pub chains. Any outlet taking on the product must sign up to 'orange serve', branded glassware, etc. The product is being imported by Coors Brewers Limited.
It is currently only available packaged, with draught trials being planned.
Incidentally, it is the same product as Rickards (until recently, both were brewed in Molson's Montreal brewery) - only packaged different. MillerCoors have taken Blue Moon production out of Montreal, to their breweries in Colorado and North Carolina.