Parliament’s role in ratifying treaties states:


The Government makes treaties…

The UK Government is responsible for negotiating, signing and ratifying the 30 or so
international treaties involving the UK each year.

The starting point for treaty ratification in the UK is that the Government has the power to make international treaties under its prerogative powers. But this cannot automatically change domestic law or rights, and – as the Supreme Court recently ruled in the Miller case – it cannot make major changes to the UK’s constitutional arrangements without Parliamentary authority.

…but Parliament has a limited role

Parliament (and/or the devolved legislatures) is therefore involved if domestic law needs to be changed in order to implement a treaty – but this does not give Parliament the power to approve, reject or amend the treaty itself. It also now has the opportunity to say that a treaty should not be ratified, but it does not have to debate or vote on most treaties.

This is in contrast to some other countries, where parliaments are involved in treaty making and may need to give their consent before ratification (often because treaties can
automatically be part of domestic law that can be relied on in domestic courts).

The 2010 Act: new power for the Commons to block ratification Part 2 of the constitutional Reform and Governance Act 2010 requires the Government to lay before Parliament most treaties it wishes to ratify, along with an Explanatory Memorandum.

This gave statutory form to part of a previous constitutional convention on
parliamentary involvement with treaties (the Ponsonby Rule).

The UK is a ‘dualist’ state

The corollary of the Government’s dominant role in making and ratifying treaties is the fact that treaties cannot change UK domestic law.

The UK is a ‘dualist’ state, which means that treaties are seen as automatically creating rights and duties only for the Government under international law.

When the Government ratifies a treaty – even with Parliamentary involvement – this does not amount to legislating. For a treaty provision to become part of domestic law, the relevant legislature must explicitly incorporate it into domestic law.

Monist’ states

By contrast, in ‘monist’ states (such as the Netherlands, for example) the act of ratifying an international treaty can automatically incorporate it into domestic law. International law is domestic law – or may even take precedence over it – and treaties may even be enforceable in the national courts as soon as they are ratified.

This approach usually involves the legislature in the ratification of treaties, as treaties are another form of domestic law.

Legal effect of treaty provisions

Treaty provisions that are not incorporated into domestic law can have only indirect domestic legal effect at best. For example, where legislation is capable of two interpretations, one consistent with a treaty obligation and one inconsistent, then the

courts will presume that Parliament intended to legislate in conformity with the treaty and not in conflict with it.

A recent post on the UK Human Rights blog gives more examples:

Customary international law is considered to form part of the common law (see Keyu).

It has been established that an international convention may be used as an aid to statutory interpretation (see Assange at [122]), particularly when it comes to human rights (see Stevens at [55ff]), or be something to which the court can have regard in the exercise of judicial discretion (see Morgan v. Hinton Organics, concerning the Aarhus Convention principle that costs in environmental litigation should not be prohibitively expensive).

An international obligation may also have become part of EU law and thus have some direct effect in the UK via that route, although this is a path that will presumably be
closed down following Brexit.