Working on the side...

Hi... Like many people I'd like to do the odd "job on the side" to boost my income whilst keeping my full time job without complications. My employer is happy for me to do this and I can get the work but what do I need to do tax-wise?

I've searched high and low (mainly on Google) to find advise on what to do and HOW to do it but nothing seems to answer my main concern... How do I avoid the tax man getting the hump with me.

So my question to you all is... Can anyone give me a basic step by step guide to what I need to do?

I figure it's something along the lines of...
1. get some work
2. tell the tax man I'm doing it
3. calculate how much I owe
4. pay the taxman
5. start the next job

But I really could do with some help on each point.

Thanks
John