You MUST have public liability insurance unless you wanna risk losing your house! and you must (should!) declare all earnings above £8.5K (or am I getting that confused with capital gains tax??!)
weldequip
He may be an idiot, but if your books don't turn out so well, he'll give you working tax credit which you can get if you're self employed. Like I say do your books right, make all the allowances you can (and you'd be surprised what you can get on there, and they will give you money!!!!