The Act was passed as a reaction to the European Union (Amendment) Act 2008, which had in the United Kingdom and Gibraltar instituted the Lisbon Treaty with no participation by the Labour Prime Minister of the day, Gordon Brown and with no referendum,[1] although one had been promised in 2005 in the Labour manifesto.

An effort led by Conservative William Hague to add a requirement for a referendum was defeated by the Labour government by 311–248 in the House of Commons.

[4][5] Cameron then promised if he won the next election he would introduce a “sovereignty bill” and amend the European Communities Act 1972 to include a "referendum lock" on further changes.

[6] Following the outcome of the election the Conservative–Liberal Democrat coalition agreement pledged in 2010: The Queen's speech reaffirmed that legislation would be introduced "to ensure that in future this Parliament and the British people have their say on any proposed transfer of powers to the European Union".

The Act also enabled ratification of a transitional protocol relating to the number of members of the European Parliament.