Governed by non-binding agreements,[7][a] the CTA maintains minimal border controls, allowing easy passage for British and Irish citizens with limited identity documentation, albeit with some exceptions.

[12] The Irish Free State officially seceded from the then United Kingdom of Great Britain and Ireland in December 1922, at a time when systematic passport and immigration controls were becoming standard at international frontiers.

[14] Before the creation of the Irish Free State, British immigration law applied in Ireland as part of the United Kingdom.

With the imminent prospect of the secession of most of Ireland from the United Kingdom in 1922, the British Home Office was disinclined to impose passport and immigration controls between the Irish Free State and Northern Ireland, which would have meant patrolling a porous and meandering 499 km (310 mi) long[15][16] land border.

The Department of Home Affairs in the newly established Irish Free State was found to be receptive to continuing with the status quo and an informal agreement to this effect was reached in February 1923: each side would enforce the other's immigration decisions and the Irish authorities would be provided with a copy of Britain's suspect-codex (or 'Black Book') of any personae non gratae in the United Kingdom.

The CTA was suspended on the outbreak of the Second World War in September 1939, and travel restrictions were introduced between the islands of Great Britain and Ireland.

After the war, the Irish re-instated their previous provisions allowing free movement,[21] but the British declined to do so pending the agreement of a "similar immigration policy"[22] in both states.

[30] In July 2008, the UK Border Agency (the predecessor of UK Visas and Immigration) published a consultation paper on the CTA that envisaged the imposition of immigration controls for non-CTA nationals, and new measures for identity checks of CTA nationals, as well as an advance passenger information system, on all air and sea crossings between the islands of Ireland and Great Britain.

This led to controversy because Northern Ireland is part of the United Kingdom, and a prominent Unionist described the proposed arrangements as "intolerable and preposterous".

[31] The nature of identity checks between Northern Ireland and Great Britain was characterised by the British Government as follows: Section 14 of the Police and Justice Act 2006 introduced a new power that will allow the police to capture passenger, crew and service information on air and sea journeys within the United Kingdom.

[35] The relevant clause was re-introduced by Home Office minister Phil Woolas in the Public Bill Committee in June,[36] but again removed in July after opposition pressure.

[44] However, the Irish and British governments and the President of the European Council have stated that they do not wish for a hard border in Ireland, taking into account the historical and social "sensitivities" that permeate the island.

[46] In October 2016, the British and Irish governments considered in outline a plan entailing British immigration controls being applied at Ireland's ports and airports after Brexit, so that Britain might control migration by EU citizens (other than Irish nationals) across the open border into the United Kingdom.

[7] The document was signed in London before a meeting of the British-Irish Intergovernmental Conference, putting the rights of both states' citizens, already in place under the Common Travel Area, on a more secure footing.

[7] The agreement, which is the culmination of over two years' work of both governments, means the rights of both countries' citizens are protected after Brexit while also ensuring that Ireland will continue to meet its obligations under EU law.

The COVID-19 pandemic led to both the British and Irish governments implementing a series of measures restricting or imposing additional conditions for entry into each other's jurisdictions.

[12] Although formally this applies only to people other than Irish and British citizens, both of the latter groups are effectively covered as they may be required to produce identity documents to prove that they are entitled to the CTA arrangements.

While in theory both Irish and British citizens are entitled to arrive here free from immigration control by virtue of the common travel area, increasingly in practice such passengers who arrive by air from the United Kingdom are required to produce their passports (or, at least, some other form of acceptable identity document) in order to prove to immigration officers that they are either Irish or British citizens who can avail of the common travel area.

INIS staff would be responsible for performing all "in-booth" duties (including examining arriving passengers), but would not take part in any matters related to restraint, detention or arrest.

"[63] As of April 2018 the only regular commercial air service between the Isle of Man and an airport outside the Common Travel Area is Geneva in Switzerland.

[65] However, as the Channel Islands has VAT-free status, the UK Border Force carries out selective customs checks on travellers arriving from there.

As in most countries, airlines may require photo identification (e.g. a passport or a driving licence) for internal flights between destinations within the UK.

Unlike the Schengen Agreement, the CTA currently provides no automatic mechanism for the mutual recognition of leave to enter and remain, and the UK and Ireland operate separate visa systems with distinct entry requirements.

Under Irish law, all British citizens—including Manx people and Channel Islanders, who were not entitled to take advantage of the European Union's freedom of movement provisions—are exempt from immigration control and immune from deportation.

[93] In support of this, the British Government is committed to ensuring that, now that the UK has left the EU, appropriate and comprehensive provisions continue to be in place for the recognition of professional qualifications obtained in Ireland.

[93] Both Governments have also committed to taking steps to ensure that British and Irish citizens pursuing further and higher education in the other state, will continue to have the right to qualify for student loans and support under applicable schemes and eligibility conditions.

The British and Irish Governments have concluded a bilateral agreement to ensure that these rights will continue to be protected now that the UK has left the EU.

[93][98] In 1985, five member states of the then European Economic Community (EEC) signed the Schengen Agreement on the gradual phasing out of border controls between them.

The Amsterdam Treaty, drafted that year, incorporated Schengen into EU law while giving Ireland and the UK an opt-out permitting them to maintain systematic passport and immigration controls at their frontiers.

The wording of the treaty makes Ireland's opt-out from eliminating border controls conditional on the Common Travel Area being maintained.