There are two kinds of general European Union laws. EU Regulations are directly effective in all member states. In the UK, this is recognised by Section 2(1) of the European Communities Act 1972, which provides that:
All such rights, powers, liabilities, obligations and restrictions from time to time created or arising by or under the Treaties, and all such remedies and procedures from time to time provided for by or under the Treaties, as in accordance with the Treaties are without further enactment to be given legal effect or used in the United Kingdom shall be recognised and available in law, and be enforced, allowed and followed accordingly...
EU Directives are not directly effective, and need to be enacted in each member state in order to achieve the goal set out in the Directive. In the UK, this is sometimes done by primary legislation (Act of Parliament), which is, for example, how the Trade Marks Directive (89/104/EEC, later repealed and replaced by EU Directive 2008/95/EC and then further amended by Directive (EU) 2015/2436) was implemented as the Trade Marks Act 1994.
But a Directive can also be implemented by secondary legislation - a Statutory Instrument in the form of an Order in Council, which receives only minimal Parliamentary scrutiny. The power to do this is set out in Section 2(2) of the ECA, which provides:
Subject to Schedule 2 to this Act, at any time after its passing Her Majesty may by Order in Council, and any designated Minister or department may by order, rules, regulations or scheme, make provision—
(a) for the purpose of implementing any EU obligation of the United Kingdom, or enabling any such obligation to be implemented, or of enabling any rights enjoyed or to be enjoyed by the United Kingdom under or by virtue of the Treaties to be exercised; or
(b) for the purpose of dealing with matters arising out of or related to any such obligation or rights or the coming into force, or the operation from time to time, of subsection (1) above;
and in the exercise of any statutory power or duty, including any power to give directions or to legislate by means of orders, rules, regulations or other subordinate instrument, the person entrusted with the power or duty may have regard to the objects of the EU and to any such obligation or rights as aforesaid.