You might be able to claim housing benefit or universal credit (housing costs) to help pay your rent but payment can’t be made before your tenancy starts. If your landlord asks for rent in advance before your tenancy starts, you’ll need to find this money from somewhere else otherwise you will be behind with your rent from the start. There may also be a delay while your claim is assessed.
If you have made a new claim for housing benefit and you have given the council all the information it needs you can ask for a payment on account after 14 days. This is likely to be less than the rent you owe but your landlord may be more likely to wait if s/he can see that you are doing everything you can to get the claim processed quickly.
If you are receiving housing benefit, you could make a claim for discretionary housing payments (DHPs) for help with rent in advance. It is up to each council to decide if they should give you a DHP and you are only likely to be awarded one if you can show that you cannot afford the rent in advance yourself. The Council will expect you to give them enough information about your financial circumstances so that they can assess whether they should help you.