Full time employed & now considering part time self employment too

I have been employed full-time at my current job for over 10 years and continue to pay my full taxes and National Insurance contributions. I am now considering additional part-time work, such as van driving or food delivery. Since I already pay taxes on my full-time employment, do I need to pay additional taxes on self-employment income? Do I need to inform HMRC about this self-employed work, and will it change my tax code? A friend who does part-time Uber Eats delivery mentioned that if the annual income is under £1,000, it doesn’t need to be declared to HMRC, but anything above that should be notified. Is this correct, considering I am already employed full-time and now looking at extra part-time work?

Hi Nas,
If your gross self employment income will be greater than £1000 in the tax year then you will need to register as self employed and complete a Self Assessment tax return at the tax year end:
Check how to register for Self Assessment
If below this threshold you will not need to register and declare. 
Please see help here:
Tax-free allowances on property and trading income
Thank you.