I think have got most things into place (which probably means i am a long way off yet

), now it's time for the 'scary' part.
I am going to be running my business in my spare time, whilst working a full time job 8am-5pm Monday to Friday.
Do i register my business as self-employed, and how would this affect my tax and NI?
Also, should i inform my current employer that i have another 'job'? - I'm not going to be burning the candle at both ends, and I'm not in competition with my employer, so it won't affect me at work. My personal opinion is that i don't need to tell them, just like i wouldn't necessarily tell them if i was selling something on eBay, or doing a car boot sale to sell of my unwanted wares? What do you guys recommend?