The Revival of European Integration (the mid-1970s to the late 1980s)

The Virtual Resource Centre for Knowledge about Europe (CVCE) is a resource centre for the study of the EU. It contains links to multimedia resources relating to the history of European integration, including coverage of key historical events such as the Fontainebleau Summit and the Genscher-Colombo Plan.

http://www.cvce.eu/home

The Europa website provides a historical overview of the period 1970-1979 and 1980-1989.

http://europa.eu/about-eu/eu-history/1970-1979/index_en.htm and http://europa.eu/about-eu/eu-history/1980-1989/index_en.htm

The Europa website provides an overview of the Single European Act: https://www.europarl.europa.eu/about-parliament/en/in-the-past/the-parliament-and-the-treaties/single-european-act

The 1985 White Paper on Completing the Internal Market (also known as the Cockfield Report) can be found at:
http://europa.eu/documents/comm/white_papers/pdf/com1985_0310_f_en.pdf 

The Jacques Delors Institute is a think tank founded in 1996 by the eponymous former European Commission President. It publishes papers on a range of issues related to European integration.

https://institutdelors.eu/en/

The Hertie School Jacques Delors Centre is named for the former European Commission President. Its researchers aim to provide an independent, non-partisan view of European policy.

https://www.delorscentre.eu/en/

The Jacques Delors archive is held as part of the Historical Archives of the EU by the European University Institute (EUI). An inventory of the archive, and digital to access to some of its key documents, is available via the EUI website.

https://www.eui.eu/Research/HistoricalArchivesOfEU/News/2016/01-19-Inventory-of-the-Jacques-Delors-archives-available-online

The Margaret Thatcher Foundation website contains a searchable database of speeches, press releases, and statements, including documents relevant to the negotiation of the British budget rebate.
http://www.margaretthatcher.org