It is standard practice in the UK to pay a deposit to the landlord in advance of moving into your rented accommodation. This is normally equivalent to one or two months' rent, but the exact amount may vary. Make sure you get a receipt for any deposit or fees you pay.
The landlord should refund the deposit in full when you move out, unless there has been damage to the property or its contents during your tenancy. Your landlord must not make deductions from the deposit for fair ‘wear and tear’, ie, the normal deterioration of fixtures, fittings and items which occurs through normal use during your tenancy.
It is advisable to keep a written record of all the rental payments that you make. If you have problems with your landlord, you can get advice from the Citizens Advice Bureau, which has rental specific guidance here.
Your landlord is legally required to put your deposit into one of the government-backed Tenancy Deposit Schemes. This ensures that your deposit will be protected if your landlord refuses to refund it without good reason or makes unreasonable deductions. Every scheme provides a free dispute resolution service. If you disagree with your landlord about how much of the deposit should be returned, the dispute resolution service will resolve the matter and refund the appropriate amount of your deposit.