A holding deposit is a deposit that is placed on the property by a tenant to show they are very interested in renting the property and wish to "reserve" it.
The holding deposit is equivalent to one weeks worth of rent and if you proceed with the tenants, it is put towards the tenants first months' rent.
The security deposit is requested from the tenant once the contract is signed. The security deposit is capped at a maximum of five weeks worth of rent in England and is held in a government approved deposit protection scheme for the full term of the tenancy.
More information:
-How will the holding deposit be treated?