During the time-limited implementation period, EU law will continue to apply in the UK subject to the terms set out in the Withdrawal Agreement. After the implementation period, all laws in the UK will be passed by our elected representatives in Belfast, Cardiff, Edinburgh and London. The Political Declaration recognises that the UK may choose to align with the EU's rules in relevant areas to facilitate trade in goods or security cooperation.
In the unlikely event that the backstop were to come into effect, a small fraction of EU rules applying today would apply in Northern Ireland, and EU rules on state aid would apply in the UK. However, as the Withdrawal Agreement and the Political Declaration make absolutely clear, we do not want or expect the backstop to be needed – and even if it ever were ever to come into effect, it would be strictly temporary.
The Official Journal of the European Union publishes upcoming EU legislation for implementation.