The Union Customs Code (UCC) is part of the modernisation of customs and serves as the new framework regulation on the rules and procedures for customs throughout the EU.
On 2 March 2018, the EC proposed that Customs authorities and economic operators be allowed to continue using already existing systems for the completion of certain customs formalities until 2025 at the latest. While most of the new or upgraded electronic systems that are necessary to apply the provisions of the UCC will be operational by 2020, some electronic systems may not be fully completed until 2025. Therefore this proposal would ensure that, in the case of the small number of customs formalities to be managed by the electronic systems that will not be completed by 2020, already existing electronic systems or paper-based procedures can continue to be used until the new systems are ready.
Full details of the latest proposals here
More on the background of how UCC affects UK importers and exporters here