Its exactly this that has led to destitution, food bank use and increase in poverty.
People get nothing for a set period, they take an advance, that in turn leaves them short for a whole year.
As sickening as it sounds, the best you can do is to try and get through it as best you can. Sell stuff, ask for food bank referral, talk to cab about advice on lowering outgoings.
Eventually it levels out but be prepared to adjust your outgoings. We live on £1000 a month to pay rent, council tax, gas, electric, etc etc. It covers bare bones essentials, but fun and treats are a once every couple months kind of deal.
Also, BE WARNED... Childcare is also paid in arrears.meaning you'll have to pay the first month's child care and claim it back the following month.
Also also BE WARNED... Depending on what job you get it will affect how often you are paid. If you get a weekly paid job, several times a year you will get 5 week's pay in a month and your UC claim will automatically end and you'll have to reckon the month after so you'll have to save up for the months you get nothing.