On entering a tenancy agreement, all tenants and any guarantors are bound by its terms. Tenancy agreement terms by their nature usually include the stipulation that these parties are jointly and severally liable for any payments arising under the agreement. Effectively, this means that while each tenant or guarantor is responsible together with every other tenant or guarantor for those obligations (e.g. one tenant is responsible for their share of the rent), they can also be legally liable for the whole obligation by themselves (i.e. the whole rent).
Combined with the flatfair service, all tenants and/or guarantors are therefore jointly and severally liable for any end-of-tenancy charges under the terms of their plan.
For example, a tenant may be up to date with making payments for their rent share but they are still liable for any arrears accrued overall due to their overall responsibilities within the tenancy agreement. As such, if there are charges owed at the end of the tenancy, all parties will be jointly and severally liable for them. It is the responsibility of the tenants and/or guarantor to resolve any issues amongst themselves as to who will settle this.
If you are unsure of the terms of your Tenancy Agreement, you should contact your managing Agent or take independent legal advice.