Also UC may berthed amount the government has decided you need to live on" but the rent component is based on your Local Authority Housing Allowance which is often at least a couple of hundred pounds shy of actual local rents. If all you get is standard personal allowance on top of the rent allowance, you have to top up the rent from that allowance and pay your bills which is nigh on impossible.
You can apply for council tax relief and Discretionary Housing payments on top, again at the discretion of the LA. It all takes time. If you get the advance payment from UC to plug the gap before UC starts paying, it gets taken back at perhaps 40.00 a month until it's paid off if it's the full amount. This is how you end up spiralling into debt.
Yes, ideally this would be a temporary situation and should incentives one to find better paying work. However if you're struggling to do that, have Housing issues etc, it becomes a nightmare very quickly, especially if your circumstances are complex.
Speaking from bitter experience.