Originally Posted by
Jonny Wilkinson
Registering with the tax man as self-employed for a secondary income is the correct way to go. You can call them and ask what the correct procedure is and what the implications are. They'll almost certainly expect you to fill in a self-assessment next year though, even if you decide not to do the work.
You'll also need permission from your main employer to allow you to do the work if you have an employment contract with them.
If you set up a company and so on, you will need to demonstrate where the labour is coming from, register with companies house, register for VAT, get and accountant, pay corporation tax on profits etc. etc..
As the labour to generate company income is coming from you, it will be treated as employment and you will need to pay NI and tax to the taxman for the employment labour and get registered for RTA payroll. Add on accountancy fees and you'll be looking at 700-1000+ per annum.
Using an umbrella company would probably be a bad thing for you as you would need to pay the umbrella company AND still have to pay all the other stuff like NI and tax etc.