Henry McMahon, the British high commissioner of Egypt, sent communications to the Sharif of Mecca that the region of Syria would be formed into an independent Arab nation. This communication was widely interpreted in different ways; the Sharif took it to mean that Britain favored an independent Arab kingdom, while Damascus intellectuals interpreted it as advocating for a democratic Arabic republic.

McMahon's statements were backed by similar insinuations and communications made by T.E. Lawrence and David Hogarth. In essence, the British commanders and leaders in Egypt were making these remarks, and the Arab leaders took them to constitute formal agreements.

And here is where perfidy arises from a global empire with considerable lack of co-ordination between departments (namely the Egyptian vice-royalty, the British Army, and the Foreign Office). Sir Mark Sykes had an entirely different idea- the Sykes-Picot agreement, which would divide Syria, Iraq, and Palestine into respective British and French mandates (and Russia would pick up Armenia and Eastern Anatolia).

So the British officials in the theater were in contradiction of the plans of London, though this was a matter of insufficient communication, not mutiny. Indeed, McMahon resigned over the public revelation of the Sykes-Picot agreement, which contradicted and contravened what he and General Allenby had publicly stated.

Essentially, there was a bureaucratic war within the Foreign Office between the pro-Arabists (McMahon, Lawrence, Allenby) and the imperialists (Sykes, Churchill, Balfour, and Townsend), and the imperialist faction prevailed in the Lloyd George government, resulting the declarations being declared as 'wartime propaganda'.

Source: Eugene Rogan, The Fall of the Ottomans