Tenants may ask to pay the deposit in instalments but landlords do not have to accept this arrangement. If tenants request to pay the deposit in this way, it may be an indication that they are having financial difficulties.
If the landlord is happy to allow it, they must still comply with the law and secure the part of the deposit they have received within 30 days.
All three of the deposit schemes will allow you to do so, either by:
Protecting the full deposit yourself and recouping the money from the tenant as they pay their instalments.
Paying any admin charges to the deposit scheme to amend the amount of the deposit protected as you receive it. You should serve new paperwork to the tenant each time you do this.