These were £4 a few weeks ago but now reduced online to £2.10.
However, check your local store as I bought some today and the yellow shelf label had them marked at £1, but, there is a 30% promotion on outdoor items at the minute so got them for 70p!
Great stuck inside your gloves when out walking the dog in winter.
They also have the Foot Warmers, 5 pair pack for £2.80, I think these were 50p for single pairs instore today, didn't see the multi pack ones.
These are normally use once items but I have seen YouTube vids showing how to reactivate them, although I have yet to try it.