It is normal for property managers to require you to pay a security deposit at the time of booking or before you move in. Where a deposit is required and you are signing a tenancy agreement, your property manager must protect your deposit in a legally recognised tenancy deposit scheme. As long as you look after the property and have no deductions for damage or unpaid rent, your deposit will be returned to you after your tenancy agreement ends.
Tenancy deposits are legally capped at five weeks’ rent per person, so if your own portion of the rent is £100 per week, the maximum deposit would be £500. It is more common however for student deposits to be in the £100-250 range.