http://en.wikipedia.org/wiki/British_Mandate_for_Palestine
The British Mandate for Palestine, also known as the Palestine Mandate and the British Mandate of Palestine, was a legal instrument for the administration of Palestine, the draft of which was formally confirmed by the League of Nations on 24 July 1922 and which came into effect on 26 September 1923.[1] The document was based on the principles contained in Article 22 of the draft Covenant of the League of Nations and the San Remo Resolution of 25 April 1920 by the principal Allied and associated powers after the First World War.[1]
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The preamble of the mandate declared:
Whereas the Principal Allied Powers have also agreed that the Mandatory should be responsible for putting into effect the declaration originally made on November 2nd, 1917, by the Government of His Britannic Majesty, and adopted by the said Powers, in favour of the establishment in Palestine of a national home for the Jewish people, it being clearly understood that nothing should be done which might prejudice the civil and religious rights of existing non-Jewish communities in Palestine, or the rights and political status enjoyed by Jews in any other country.[3]
I still don’t follow how that links to your argument about “promises immediately broken.” As far as I can see, the preamble makes the position of the British utterly untenable, given the demands of the Muftis on one hand and the Zionists on the other.