Diplomacy: Theory and Practice, 6th ed.  –  Online updating pages

Chapter 2: Prenegotiations

p. 23, prenegotiations defined: a broader sense of this term seems to have emerged (the usage is predictably loose) in a paper published by the UK government in 2018 (see Further reading below). Here it appears to be using the term to embrace discussions with interested parties in the UK itself (‘stakeholders’) preparatory to engaging in further prenegotiations with foreign states in launching its much-heralded ‘independent’ post-Brexit international trade policy. This might have entitled the term to a ‘sense (2)’ in our Palgrave Macmillan Dictionary of Diplomacy because wise liberal-democratic governments have always negotiated with domestic interests in a bid to ensure that the implementation of their policies is not sabotaged. Nevertheless, I don’t believe that this sense is in common usage, so it is probably best avoided.

Further reading
Major, Sir John, Witness before the Northern Ireland Affairs Committee of the UK Parliament, Tuesday 7 February 2023, viewing time two hours.
Major was the Conservative Party British prime minister from 1900 until May 1997 and intimately involved in the prenegotiations (broadly conceived) of the Good Friday Agreement that was finally signed by his successor, Labour Party prime minister Tony Blair, a year later. In an opening statement, Sir John gives a very lucid and interesting account of the diplomatic spadework from which Blair benefited, and then answers questions. In the course of these he also takes some well-aimed swipes at the ‘colossal mistake’ of Brexit, pointing out that, among other things, common membership of the EU by Britain and the Irish Republic had made possible many private meetings for him with the Irish prime minister, Albert Reynolds, from 1992 until 1994.

UK Government, ‘Pre-negotiations phase of trade negotiations – approach to stakeholder engagement’, 6 August 2018