Argos in Sainsbury's stores allow Click and Collect as they did under lockdown. The stand-alone Argos stores are closed. (I was looking for a gift today from someone so was seeing what shops were open.)
I don't use B&Q I use Wickes, Toolstation and Screwfix. Regardless all DIY stores are regarded as essential retailers so should be open. Wickes were doing Click and Collect under lockdown. Toolstation and Screwfix you are supposed to do Click and Collect now as they don't want people touching their in-store catalogues.
Poundland sells bread, milk and random other human food plus pet food so they like Wilkos, who sell similar food products, are classed as essential retail. They were both open under lockdown.