Non essential shops closed, clothes , electrical etc. Nothing about trade supplies, so still trading.
No mention of building sites closing, many of trades are self employed and nothing mentioned of helping them out, so carry on.
I suspect once the self employment issue has been sorted, then the sites will be closed.
Essential is food and medicine. Not building materials ! Police and council will be out tomorrow closing things up
The FT specifically says hardware stores will remain open - but I don't know where they got this information from. "Most shops will close with immediate effect, with only “essential” stores such as food outlets, pharmacies, petrol stations, post offices, hardware shops and newsagents allowed to stay open. Banks will also be allowed to keep their doors open." https://www.ft.com/content/cad58520-6d2e-11ea-9bca-bf503995cd6f
I do wish they'd stop simply referring to supermarkets and 'food outlets'. My local greengrocers is essential (but not a supermarket), whereas the kebab house is a 'food outlet' but not essential. I must admit I'm surprised that there was not a detailed list of these sorts of things to accompany the announcement - they must have anticipated this sort of question.