If your working for a contractor of any sort they will take 20% of your earnings under the cis scheme, you will still need to do a tax return though and that will probably result in a rebate as all your expenses will now come off the tax you’ve already paid at source. All your fuel, vehicle expenses, work clothes, tools, mobile phone can all be claimed back. You will also need to register for NI, best bet is to speak to an account but it’s all pretty straightforward especially if your working for one person and not loads of different customers.