OP:
Someone may "get away" with earning some small amount of cash and not declaring it for tax - and when i say small I am thinking of like £1,000 or less in a year -- so its a hobby income!
But if you are living on benefits, then it isn't worth taking risks.
And if you are earning a substantial sum - that is enough to pay your bills, you have to register as self-employed, keep records.
There is no way to keep this income secret from the Inland Revenue over the long term.
Really - the easiest way to manage it is to speak to an accountant.
* End the benefits ASAP - if they are MEANS TESTED and you aren't really entitled to them.
* Contact the inland revenue and tell them you will be self-employed as --- some kind of therapist - or have the account ant do that for you.
* When you contact the Inland Revenue they will ask you to estimate what your income will be and when you are starting this business so think about your answers - although you should be honest and go back to whenever you started... perhaps you might decide to say you have just started it now- ty and get yourself straight going forward and hope no one looks into the past -- IDK if that will work but it is better than carry on hoping to get away with it - you could face prison.
I would suggest you underestimate your income because they ask you to pay Income Tax in advance, so that's a big tax bill straight away - eventually, the tax will even itself out.