I've swum the murky waters before with UC, mostly when starting out self-employed and went to claim working tax credit during a period of low income. Those tax credits turned into UC, and UC hates the self-employed to the point where advisors say you oughta pack it in completely unless you're doing well enough not to ever claim.
Personally I did just that and went back to temporary contracts on PAYE. You can expect your benefits to be decimated if you get your pay during the 'payment periods' taken into account with UC. I did a short contract that ended just after Christmas, but because of the holidays then payroll were late. Because of that it fell into UC's zone of consideration and I therefore lost the vast majority of my December pay coming off February UC's, because I got December's pay late in January. That was a hard couple of months.
Since then I've binned off short term contracting and my old career specialism of 5 years entirely, and UC is partially the reason for that. You'd think the whole system was designed by an idiot, but it was actually designed for a specific purpose - to skim off as much from the benefits bill as possible while showing claimants have the same entitlement or better than on JSA/housing benefit, but in reality that's only true in the most simple of circumstances (long-term unemployed who never earns a penny or those who work in a steady part time job on PAYE and are paid monthly - anyone else is entering a minefield if they have to claim UC).
I remember years ago when JSA gave me a grant to start my own business and paid unemployment until it was up and running. I ran it until I was paid more salary and I'm wondering how UC is supposed to consider this?
It's worrying to think that I wasn't given much but able to show my potential in the field I specialised in, compared to penalising those who wish to better themselves and work on their own business.