It seems that you have to earn a certain amount or everyone would be claiming to be self-employed for x hours but not turning a profit or much of one. A few people would lie, most would actually be working, but have costs which would bring profits down or well, be trying to earn a living in, oh what's that thing called again, IDS - oh yes; a RECESSION.
I posted this earlier on the subject of childcare:
CMs are self-employed, can only make so much due to age / ratio restrictions and crucially, have to spend money. Professional training, food, fees for playgroups, toys, craft materials needed in order to deliver the early years curriculum. Most of these would be tax deductible, surely? So you will be unlikely to make a profit equivalent to NMW.
If I am correct, then only people who will be able to afford losing tax credits under UC will be those who have high-earning husbands. OR fees will have to rise. So it might well be that finding affordable and available childcare will become even more of a problem for everyone.
I can well imagine quite a few formerly self-employed people having to do workfare INCLUDING childminders. That'll help 
It's completely unworkable. How much does IDS get paid? It's a shit idea and he is clearly incompetent. Sack him and save the country a few quid. My consultancy fee is very reasonable.