Many many business remain open and we need them to operate. They are not banned from going to work and cannot work from home. They will carry on working and get paid.
On which businesses must close it is a limited list - if you are not on it then you do not have to do so it seems to say
On which must close the following is useful:-
assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/874732/230320_-Revised_guidance_note-_finalVF.pdf
eg lots of shops must close but garages and vets can open as can hardware shops, launderettes, dry cleaners, post offices, banks, newsagents. If you live at a caravan park as many do you can continue to live there.
Places of worship can remain open for solitary worship and for live streaming of a service without parishioners there. Otherwise only funerals with immediate family present are allows.
This presumably means the Prime Minster's child will be born out of wedlock unless they can fly to a country that allows weddings!!!! Baptisms are banned (even if in your religion a child goes to Hell if it dies before being baptised)
The way they have done it is if your business is not on the banned list you can remain open.
In terms of timing this new list is not law yet
"As of 2pm on 21 March 2020, closures on the original list [ they mean not the list issued yesterady] from 20thMarch are now enforceable by law in England and Wales due to the threat to public health. The government will extend the law and enforcement powers [ they mean the list I link above it not yet the law ] to include the new list of premises for closure. Further measures on enforcement could be taken following the passage of the Coronavirus Billthrough parliament."