Right, I did some work that I wasn't expecting payment for. My client (an old employer) agreed to pay me £200, but I need to know how to get it through the books.

I am employed full time but may try to get a few more wee projects over the coming months.

So my questions:

1). Do I need send an invoice?
2). If so, does it need to come from a registered company and do I need to register as self-employed/sole trader
3). Do I need to register a company?
4). Do I need a company bank account?

Thanks in advance!