R (Jackson) v Attorney General [2005] UKHL 56 is a House of Lords case noted for containing obiter comments by the judiciary acting in their official capacity suggesting that there may be limits to parliamentary sovereignty, the orthodox position being that it is unlimited in the United Kingdom.

The case, brought by Jackson and two other members of the Countryside Alliance, challenged the use of the Parliament Acts 1911 and 1949 to enact the Hunting Act 2004. The appellants claimed that this Act was invalid as it had been passed using a legislative procedure introduced by the Parliament Act 1949 which allowed Acts of Parliament to be passed without the consent of the House of Lords if they had been delayed by that chamber for a year. This claim was based on the argument that the enactment of the Parliament Act 1949 was itself invalid, as it had been passed using a similar procedure introduced by the Parliament Act 1911.

A divisional court and Court of Appeal both rejected this claim, although the Court of Appeal held that Parliament Acts procedure could not be used to effect "fundamental constitutional changes". The case was appealed again to the House of Lords. In relation to preliminary issues, the court held that it had jurisdiction to examine the validity of the Hunting Act as a question of statutory interpretation (whether the 1911 Act could be used to enact the 1949 Act); standing was not challenged. On the substantive issue, the court ruled there were no limits to the type of legislation that could be passed using the Parliament Acts except for the express limitations contained in the legislation. The Parliament Act 1949 had therefore been validly passed using the 1911 Act and the Hunting Act was consequently also held to be an Act of Parliament. In obiter comments made in the judgment, Lord Steyn, Lord Hope and Baroness Hale suggested that there might be limits to parliamentary sovereignty (although Lord Bingham and Lord Carswell implicitly supported the orthodox view that there are no limits to parliamentary sovereignty).

Jackson prompted debate about the legitimacy of limiting parliamentary sovereignty and the theoretical justifications for the ruling. Alison Young suggests that the opinions could be explained by the Parliament Act 1911 modifying the rule of recognition defining valid legal documents or by the Act redefining Parliament in a manner that binds the courts. Christopher Forsyth argues that the Parliament Acts redefined Parliament to be a bicameral body for all legislation which also has a method of unicamerally legislating (except to extend Parliament beyond five years). Jeffrey Jowell proposes that there are two reasons for limiting parliamentary sovereignty – if the democratic legitimacy of the legislature were undermined by its acts or if the body attempted to remove fundamental rights in a democratic society – and cites support for these arguments from the judgment. The case was also criticised for claims made by Lord Steyn and Lord Hope that the doctrine of parliamentary sovereignty was solely a judicial creation.

In the United Kingdom, bills are normally presented to the monarch for Royal Assent after they have been passed by both the House of Commons and the House of Lords, at which point they become primary legislation as Acts of Parliament. However, bills can also be passed using the Parliament Acts 1911 and 1949. The Parliament Act 1911 allowed bills to be presented for Royal Assent without the assent of the House of Lords if they had been passed by the House of Commons in three successive parliamentary sessions and there had been a delay of two years. The Parliament Act 1949, passed using the Parliament Act procedure, amended the 1911 Act to reduce the power of delay to two successive sessions and a period of one year. The legislation defines two exceptions in section 2(1) of the Parliament Act 1911: Money Bills can only be delayed for one month and "Bill[s] containing any provision to extend the maximum duration of Parliament beyond five years" are not eligible to use the procedure.

The Hunting Bill was introduced as part of Labour’s 2001 general election manifesto pledge to hold a free vote on banning fox hunting and would make it illegal to hunt wild animals in England and Wales with dogs except in limited circumstances. The bill was passed by the House of Commons on 3 December 2002 but rejected by the House of Lords. It was reintroduced to, and passed by, the House of Commons on 9 September 2004, but was significantly amended by the House of Lords. The House of Commons rejected the amendments on 18 November and the bill was granted Royal Assent later that day through the use of the Parliament Acts. The Hunting Act was due to come into force on 18 February 2005.

John Jackson, Patrick Martin and Harriet Hughes, all members of the Countryside Alliance, sought judicial review of the use of the Parliament Acts to pass the Hunting Act. They claimed that the 1949 Act had not been lawfully passed either because the 1911 Act could not be used to amend itself or because it provided a method of making delegated or subordinate legislation which could not alter the process of legislating. Consequently, they claimed, the 1949 Act had not reduced the delay specified in the 1911 Act and the Hunting Act, which was passed only in accordance with the requirements as amended by the 1949 Act, was invalid.

The case was heard in a divisional court by Lord Justice Kay and Mr Justice Collins in January 2005. In their judgment, they found that the legislation made using the 1911 Act could modify the Act, as indicated by the reference to "any Public Bill" [emphasis in original] being permitted to use the Parliament Acts (except for a limited number of express exceptions). Furthermore, they ruled that the 1911 Act did not create a method of making delegated legislation, but was instead a redefinition of the relationship between the House of Commons and the House of Lords. Moreover, there was found to be "no established principle applicable to this case which denies a power of amendment of the earlier statute in the absence of the express conferral of one specifically dealing with amendment". The Parliament Act 1949 was therefore found to have been validly passed using the Parliament Act 1911 and the Hunting Act was consequently also held to be an Act of Parliament.