Possibly very local.(Was Harlow Edinburgh Way) but had a yellow sticker so may be widespread.
Yes Its Tesco, Yes it may just be this store and Yes it may be a wild goose chase.
Veho Pebble Smartstick battery, reduced from £15 to £3.75 in Black, Reduced to £9 in silver, and no price on the purple ones.
These are the both older tube style packaging and the newer square packaging, difference is the tube pack ones have a headphone socket on the battery and an adapter so no use for newer phones (like iPhone 5) where there is no adapter in pack, without buying more adapters, whereas the square pack ones have a USB and MicroUSB socket, so you use the adapter you got with your phone.
There were maybe half a dozen left on display at Edinburgh way, couple of black and a couple of silver and a purple one mainly the older pack type after I bought two.