I have read somewhere that if you get paid through CJ then you may not have to abide to the UK tax rules as the payment is coming from another country
Nope. What Simmo said is right : it doesn’t matter what country the source of your income comes from, as a UK citizen, you have to pay tax on it to the UK government.
You need to do two things: 1) register as self-employed. 2) File a tax return.
It might be advisable to find an accountant if you think your circumstances warrant it. You can compare quotes from local accountants here: