Both the UK and France had their own reasons from developing nuclear weapons, but these reasons make little sense today.[1] Both countries were trying to cling on to the international status they had enjoyed before their overseas empires began to disappear after WWII.[2]
After Brexit, France is now the only nuclear-armed country remaining in the EU, which has made France uncomfortable on a number of levels. First of all, France is very keen on greater EU defense integration. France pulled out of the NATO military structure under Charles DeGaulle in 1966 and supports a purely European military structure under the auspices of the EU.[3] The problem is that having nuclear weapons makes it rather complicated to just “hand over” the French military to the EU, not least because of the NPT, which forbids it.
Nevertheless, in 2020, President Macron of France tried to offer France’s nuclear arsenal to the EU.[4] This was met with a muted response, especially in the European Parliament, which supports the TPNW and has urged all EU members to join it. The German government is also committed, in theory, to exploring the option of joining the TPNW. Public opinion in most other European countries is strongly opposed to nuclear weapons.
If France wants to integrate its armed forces into an EU military structure, and if the EU doesn’t want France’s nuclear weapons, what will France do with them? At some point, it will make no sense at all for France to hold onto its nuclear weapons, especially if the UK is pushed into giving up theirs.
[1] The UK continues to depend heavily on US technology and assistance for its own Trident nuclear weapons program (see next page), but the initial impetus for the UK to develop its own nuclear weapons was the “breakdown in the exchange of information” between the US and the UK, according to Churchill, in Hansard, 1 March, 1955, p.1892. See https://www.parliament.uk/about/living-heritage/transformingsociety/private-lives/yourcountry/collections/churchillexhibition/churchill-the-orator/hydrogen/. Once the Soviets had their own Bomb, it seemed increasingly unlikely that any US President would risk destruction of the US homeland by using nuclear weapons against the Soviet Union in defense of the UK or any other European ally. But were the UK or France to launch nuclear weapons against Russia, it would be equally self-destructive.
[2] Then Foreign Secretary Ernest Bevin famously exclaimed in a Cabinet meeting where the decision was taken: “We’ve got to have this thing over here, whatever it costs. We’ve got to have the bloody Union Jack on top of it.” The formal minutes of the meeting on 8 January 1947 are printed in Documents on British Policy Overseas (DBPO), Series I, Vol. XI, No. 36, and record Bevin’s views in a more measured way. See also Peter Hennessy, The Secret State: Preparing for the Worst 1945-2010 (Penguin revised edn, 2010).
[3] BBC News. (2018, November 6). France’s Macron pushes for “true European army.” BBC News. https://www.bbc.com/news/world-europe-46108633
[4] Bugos, S. (2020, March). France Offers Nuclear Deterrent to All Europe. Arms Control Association. https://www.armscontrol.org/act/2020-03/news/france-offers-nuclear-deterrent-europe