They sell the UK version of Chicken of the Sea albacore in Partridges in Kensington. It's expensive, but pretty much like the US version. They also, in case you missed it previously in the thread, have quite a big selection of US food (even more than on their site).
They also have a generic brand of albacore (in brine or sunflower oil) in Whole Foods, but I am not sure how it is. I wish we had stopped there first because it was a third of the price of the Chicken of the Sea. For that much of a difference in cost, I would have been willing to experiment.