Hi,
It really depends how far you want to take it. If this is something you are going to be doing regularly, you can certainly look into setting your own company up.
However, the way you mentioned is also fine. You just invoice the client with instructions on how they can pay you, you then declare this at the end of the tax year (you will need to request a form from HMRC or download from their
website hosting. I think they also allow you to file online).
If you do it with the above method, make sure you don't spend all the money and leave yourself short for when you need to pay tax.