When the UK left the EU it could no longer continue to use the CE mark and any associated European legislation (such as the ATEX Directive) so had to devise its own.
The UKCA mark has been created to replace the CE mark in the UK. The majority of the existing requirements have remained the same, making achieving the certification quite simple for manufacturers of existing CE marked products. Here is a brief overview of the key differences between CE and UKCA marking.
What is UKCA marking?
UKCA is the United Kingdom Conformity Assessment that is applied to goods being placed on the market of UK. The UKCA mark is only applicable to the UK and is not accepted anywhere else.

Europe (today)
CE mark
Directive 2014/34/EU
EU Declaration of Conformity
EU-Type Examination Certificate
Quality Assurance Notification (QAN)
Notified Body
Harmonised Standards
UK (after 1st January 2021)
UKCA mark
SI 2016 No. 1107 (amended by SI 2019 No. 696)
Declaration of Conformity
UK Type Examination Certificate
Quality Assurance Notification (UK QAN)
Approved Body
Designated Standards