Whilst payment of a deposit is not a validity requirement, certain rules apply if a deposit is agreed upon in a lease

In lease agreements relating to residential property, the landlord is obliged by the Rental Housing Act to place the amount received as a lease deposit in an interest-bearing account held with a financial institution. The interest rate applicable to this account may not be less than the rate applicable to a savings account at a financial institution. The tenant may request a statement of the interest earned on the money at any time during the tenancy.

If the deposit is paid to the account of a registered estate agent on behalf of the landlord, it must similarly be invested; the deposit and any interest thereon is then dealt with in accordance with the provisions of the Estate Agency Affairs Act.