That's in the U.K. for all black teas? Certainly noticed the trend in Canada starting over a decade ago, and very evident even in very English parts of the country. I found that one of the lower-end supermarket chains (owned by the family which owns ABF and F&M) that caters to Indians carries a lot of loose leaf black tea aimed at the Indian market so you will find 1-2lb boxes/bags of Brooke Bond Red Label, Lipton Yellow Label (not bad in loose leaf, horrid in bags), and I think even PG Tips among others. I counted over 23 different varieties at a location that caters to a majority Indian clientele.

One other brand that was stocked in some stores is Ahmad Teas. The only loose leaf tea that I've found was the cardamon tea. Delicious the first time you drink it, and then it appears you become immune to the flavour and don't taste it anymore, even after months of not drinking it (still smell very cardamon-y though.