Hi
The work where you are directly on the payroll is employment. Where you are required to submit invoices, is classed as self employment. If your total invoiced in the tax year is more than £1000.00, then you will need to register for self assessment, as self employed. You can do this at
Set up as self-employed (a 'sole trader'): step by step . When completing your tax return, you declare your world-wide income, so you would include your employment income. Self assessment will calculate your tax and national insurance for your self employment.