The United Kingdom is currently scheduled to leave the European Union on April 12th, 2019 unless some other agreement is reached. If this happens, the implications for current manufacturers/suppliers of wireless/electronic apparatus are as follows:
Existing Products and Certificates
Existing EU Type Examination Certificates (TECs) issued by the US Notified Bodies (as approved by the European Commission) and the CE marked products will continue to be accepted in the UK for a time-limited period after Brexit. As such, it will not be necessary to issue separate UK TECs yet.
New UK Regulations/Directives
Initially upon entry into force, the UK regulations above reflect a direct transposition of the European Union's Radio Equipment Directive (RED) and Electromagnetic Compatibility Directive (EMCD).
Harmonized Standards
The role of standards in the regulatory framework for manufactured goods will not change when UK leaves the EU. we leave the EU. The current EU ‘harmonized standards’ will be carried across as UK "designated standards," to maintain a single standards model between the UK and the EU.
Although the UK will try to maintain sync with the EU harmonized standards, divergence between the two is certainly possible in the long term.
CE Marking and UKCA Marking
You will still be able to use the CE marking for products placed on the UK market if either third-party assessment was carried out by an EU-recognized notified body, or if the certificate of conformity previously held by a UK body has been transferred to an EU-recognized body.
You will still be able to use the CE marking for products placed on the UK market for a time-limited period, unless your product requires third-party conformity assessment. If this has been carried out by a UK "notified body," you will be required to apply the new UKCA mark.
Manufacturers (located anywhere) that are placing a product on the market in the UK and using the self-declaration of conformity process (without any need for involvement of a third party) may optionally use the UKCA mark (for the UK). The CE marking would also be accepted in the UK for a time limited period.
Please reference this for more information on the CE and UKCA marking after Brexit.