Policy and legal background
The two Church of England Archbishops and 24 of its other diocesan bishops are entitled to sit in the House of Lords as the Lords Spiritual. They do so by virtue of ancient usage and statute. Five of the 26 bishops automatically receive writs of summons to attend the House of Lords on the basis of the sees they occupy (Canterbury, York, Durham, London and Winchester; 'the five ex officio sees'). The remaining 21 are issued with writs of summons on the basis of seniority (i.e. length of tenure as a diocesan bishop) when a vacancy arises. This mechanism is set out in section 5 of the Bishoprics Act 1878.
	On 17 November 2014 the General Synod of the Church of England enacted the final legislation necessary to allow women to become bishops. However, due to the arrangements under the Bishoprics Act 1878, it would have taken over seven years before a newly appointed female diocesan bishop would have become sufficiently senior to take a place in the House of Lords (unless she were appointed to one of the five ex officio sees). Consequently, the Archbishop of Canterbury, after consultation with the Lords Spiritual and others, requested on behalf of the Church of England that amendments be made to the arrangements under the Bishoprics Act 1878 to enable the accelerated entry of female bishops to the House of Lords.
	Parliament subsequently passed the Lords Spiritual (Women) Act 2015 (‘the 2015 Act’), which came into effect on 18 May 2015. The 2015 Act modified the application of the procedure under the Bishoprics Act 1878 for a time-limited period so that vacancies among the 21 places, which are normally filled by seniority, are filled as they arise by eligible female bishops, if there are any available at that point (an eligible bishop is a bishop of a diocese in England who is not already entitled as such to a writ of summons). If there is more than one eligible female bishop then the one whose election as a bishop of the diocese was confirmed first will receive the writ. In practice, for a period of 10 years between 2015 and 2025, the most senior eligible female bishop at any time now fills a vacant Lords Spiritual seat in preference to the most senior eligible male bishop.
	The effect of the 2015 Act has been that six bishops who are women have sat in the House of Lords sooner than would have been possible under the procedure in place prior to the 2015 Act. Five of these bishops still sit in the House; one has retired.
	Male bishops have continued to enter the Lords under the 2015 Act, in accordance with the arrangements under the Bishoprics Act 1878 for determining seniority of precedence, if there were no eligible female bishops at the time a Lords Spiritual vacancy arose.
	The relevant provisions of the 2015 Act were due to expire on 17 May 2025. The Lords Spiritual (Women) Act 2015 (Extension) Act 2025 extends the provisions of the 2015 Act for a further five-year period so that the appointment process in the 2015 Act will now expire on 17 May 2030. This is designed to increase the number of female bishops sitting in the House of Lords more quickly.
	After the end of this period, the provisions made by the 2015 Act and extended by this Act will come to an end, and the arrangements under the Bishoprics Act 1878 for determining which bishops are to fill vacancies among the Lords Spiritual will be restored. The arrangements in relation to the five ex officio sees are left unchanged since any woman appointed to one of those sees will in any event become a Lord Spiritual immediately. For example, Sarah Mullally became Bishop of London in March 2018 and took her seat in the House of Lords in April 2018, outside of the provisions of the 2015 Act.