OK OP, deep breath. I'm sure this is do-able. Don't buy scratch cards or sell your body!
First thing first, workwise are you signed up to every temp agency in the area as well as applying for jobs that are advertised/permanent jobs? Have you made it clear that you are prepared to travel and work unsociable hours (nights etc) - assuming you are of course. A couple of weeks temping even at NMW should get you most of the way there - although what are you living on in the meantime if you've no income?
Any family, friends or acquaintances who may have some odd jobs that need doing (thinking gardening, ironing, babysitting, cleaning) you could do to earn some cash? I know it's not nice to have to ask but needs must. Maybe advertise on taskrabbit or similar if you are able to do that kind of work, or put a card up in local shop?
Any outgoings you can (temporarily) cut back to save some money? Sorry if this is obvious and you are already back to bare bones.
Do you have your UC appointment now? As Mc says, you can ask them there about an advance and is the money you need is for a housing deposit there may be a loan scheme in relation to this too?
If you have a small amount of capital and some time match betting can be a good way to raise a small amount of money (it is not real betting and you mustn't do it if you've ever had any gambling issues) - there is a thread on here explaining how it works...
Or other ways of quickly raising some cash - do you have anything you can sell or pawn? Jewellery, car, clothes, electronics? I know you said a loan is not possible due to poor credit but what about a credit card or overdraft (neither ideal as they'll charge interest but worth checking with your bank none the less as a short term solution)? Any family who would loan you the money on the understanding you can pay back once you get your UC backpay through?
Hope you sort it!