Whatever it says on the government website, they do not give you 100% advances in benefit. It is generally up to around 60% of what you'd get, they only advance for what they consider allowable expenses (basically food, electric, gas) - any debts or other bills you're expected to rearrange with the creditors. Most other items are not considered necessary essentials that can't be delayed until your benefit is sorted. You have to itemise what it is needed for and they calculate a percentage they will cover. Not sure if the UC budget is done the same way as old style Crisis Loans, but I've gone through the Decision Makers Guide thoroughly and most of it is very similar if not exactly the same. If budgets work the same way, you can be turned down of it is near the end of the month, just because there's no money left in their budget for the month. Even if you fulfil the criteria. You also have to show that there's nowhere else you could borrow the money from. If you have a credit card - no advance. Family who could lend money? No advance. Food bank who could offer parcels? Etc.
It is utterly shit. I have worked within the old system and former colleagues tell me the UC system and the advance system is far, far worse than the old one. I have spent almost 9 weeks with only £80odd quid in child benefit to feed us, clothe us, keep the metered lights on and keep us warm in December. An advance was refused as I hadn't yet been for my first JSA interview. I couldn't attend d an interview for almost two weeks as the jobcentre was fully booked up! When I made a complaint as my children would literally starve or die of a medical condition that requires electricity to be available, I was advised they couldn't help and I should phone Social Services and ask them to help.
I am an intelligent articulate person who has worked within the system, knows exactly what to say, what buzzwords to use on their forms and who to ring, I know the relevant legislation and their own guidance policies. What hope is there for anyone else?