Historically, most objections to the parliamentary oath have arisen from religious concerns: religious restrictions on swearing an oath, and concerns over swearing allegiance to the Head of the Church of England (a particularly problem for Roman Catholics). The wording of the affirmation was designed to circumvent these concerns, although arguably perhaps only achieves it in the first example.

Republican objections have also been raised. Recent examples include Tony Banks, who reportedly crossed his fingers when taking the oath in 1997, and Tony Benn, who has repeatedly voiced his concerns over the oath:

Former MPs attempted change through private members' bills but none made progress: Tony Benn proposed a Parliamentary Declaration Bill (13 January 1998) and Kevin McNamara introduced the Parliamentary Oath (Amendment) Bill 2000-1.

A number of MPs also object on democratic grounds - as noted above, the requirement to take the oath is contained within the Members Code of Conduct. Those failing to take the oath are penalised by the parliamentary forces (e.g. with the withdrawal of pay and allowances). Objectors argue this contravenes democratic principles since the electorate decides who it wishes to send to Parliament; it is not right therefore that those chosen people are prevented from taking their seats:

Nationalist objections

Northern Ireland

Irish Nationalists elected to the House of Commons find the oath to the monarch problematic, rejecting as they do Britain's claim to sovereignty over any part of Ireland. Welsh and Scottish nationalist parties elected to the British House of Commons do not necessarily oppose the continuation of the monarchy, and as such often have had no great difficulties in swearing an oath of allegiance to the Crown.

The case of Sinn Féin MPs illustrates a central problem with the oath, namely that it undermines the democratic principle. Sinn Féin adopts an abstentionst policy towards Westminster and cannot take part in proceedings as its MPs refuse to take the oath. Candidates that have been chosen by the electorate to represent them are prevented from performing their representative function by parliamentary procedures. In 1997 Sinn Féin launched a legal challenge against the oath, eventually appealing as high as the European Court of Human Rights, on several grounds, including: an interference with the right to freedom of expression; an interference with religious beliefs (in that the oath obliges Roman Catholics o swear allegiance to a monarch who is by law prohibited from being Catholic or marrying a Catholic); and an interference with the right to free elections, as MPs are prevented from properly representing the opinions of constituents.

The Court found the application to be inadmissible largely on the grounds that the oath is a reasonable and proportionate condition attached to elected office in light of the UK constitutional system:

"forms part of the constitutional system of the respondent State, which, it is to be observed, is based on a monarchical model of government. For the Court, the requirement that elected representatives to the House of Commons take an oath of allegiance to the reigning monarch can be reasonably viewed as an affirmation of loyalty to the constitutional principles which support, inter alia, the workings of representative democracy in the respondent State [...] In the Court's view it must be open to the respondent State to attach such a condition, which is an integral part of its constitutional order, to membership of Parliament and to make access to the institution's facilities dependent on compliance with the condition".

Scotland

Following the May 2007 elections to the Scottish Parliament, the Leader of the Minority Government, Alex Salmond, prefaced his oath with the statement that "the Scottish National Party's primary loyalty is with the people of Scotland, in line with the Scottish constitutional tradition of the sovereignty of the people.