If you receive less housing benefit as a result of the changes due to the bedroom tax, the benefit cap, or a non-dependent deduction, you can apply to your local council for a discretionary housing payment to make up the shortfall. There is only a limited fund each year, and so there is no guarantee that help will be available. If there is, the council will tell you if you are eligible, and how long the discretionary payment will last for, as it is generally only short-term. Priority is usually given to the disabled and those with chronic medical conditions. There is a set limit on the amount of discretionary housing benefit that can be paid each week. It may be possible to have payments backdated.
If you wish to apply ask the council for a claim form. You will need information and proof of your income and outgoings, such as bank or building society statements and utility bills. Any problems that make it difficult for you to pay your rent should be listed, examples include: sickness or disability costs relating to things you have to buy, travel, the need for an extra room due to illness or disability, caring for a sick relative or friend, and the risk of becoming homeless.