In particular circumstances, a public authority decision may be challenged on the grounds of proportionality. This essentially means that where a decision involves a significant interference with a person’s important legal rights (e.g. a person’s right to citizenship of the UK), or otherwise engages EU law or the European Convention on Human Rights (“ECHR”), the Court will require that any interference with a person’s rights is no greater than that which is necessary to achieve the aim of the interference.
Initially, it was considered that the principle of proportionality would only be available as a distinct ground for judicial review where a public authority’s decision involved EU law or ECHR issues. However, following a series of cases, and the case of Pham v Secretary of State for the Home Department  UKSC 19 in particular, it appears likely that any decision involving significant interference with fundamental rights will be challengeable on proportionality grounds, regardless of whether EU law or the ECHR is also engaged.
A court’s assessment of proportionality will involve the following considerations:
- whether the decision’s objective is sufficiently important to justify limiting a person’s right;
- whether there is a rational connection between the decision and the objective (i.e. whether the decision is suitable);
- whether the objective could have been achieved in a less intrusive way (i.e. whether the decision was necessary);
- whether the decision’s negative effect on a person’s rights outweighs the importance of the objective. If so, the decision will be disproportionate (i.e. whether the decision strikes a fair balance).