For single person on JSA the disregard is £5 a week. So anything you earn over this is deducted pound for pound.
If you work 16 hours a week or over I "think" you are counted as employed and not unemployed.
The rules on being worse off are very vague, but if you can PROVE you have less than the specified minimum amount to live on then generally they won't force you into it - if you just say it or give them partial proof they will ignore it. The strange exception is that CSA payments aren't taken into account - so a single person (over 25) on jsa has to live on £5 less than they say is the minimum amount they can live on.
In a time of universal deceit - telling the truth is a revolutionary act. George Orwell
When the debate is lost, slander becomes the tool of the loser. Socrates