It's not illegal to continue to have a cleaner in your home. The guidance says...
Tradespeople...must only go into someone else’s home to carry out or deliver essential work or services, for example:... domestic cleaner providing services in support of a clean and safe living environment for people in vulnerable circumstance, living with a disability or otherwise unable to clean their own home
So a cleaner is able to go into a house where there are people in vulnerable circumstances (children?), or unable to clean their own home (due to physical, mental or time/ employment constraints, presumably). The concept of cleaning being essential has therefore been established the person who wrote the guidance needs to never ever come to my house so if that can't be done by the householder it is fine to get someone in to be paid to do it. Obviously some people may prefer not to continue to employ the services of the cleaner, if they are able to provide a clean and safe living environment without help (though the cleaner may not be able to do that themselves if too many people stop employing them).
And this is guidance - the law says you can go to work if that work can't be done from home, which is pretty much cleaning by default...
The guidance does also say that when in someone’s house, tradespeople should stay 2 metres apart from the people who live there, wear a face covering and follow good hand and respiratory hygiene. So they should be wearing a mask really, though if they don't want to, and the client is fine with that i can't see anyone complaining.