The Jewish population in Palestine sided with the British during the 1st World War. Keep in mind that in 1917 when the Balfour Declaration was confirmed, Britain was in the midst of fighting the Ottoman Empire; they were not the colonial power yet. 
 Jabotinsky led the effort to cross the Jordon into what is today the coutry of Jordan. Later, he was decorated and Chaytor told the Jewish troops: "By forcing the Jordan fords, you helped in no small measure to win the great victory gained at Damascus."
Once Britain had control of Palestine they were less and less helpful to the Jewish people culminating in the White Paper and then the underground war by the Irgun etc to drive them out. 
As far as your allegation that, "creation of Israel by Britain was one of the last cases of a colonial power deciding it had the right..."
Just look up how many countries were formed in the 20th century by the colonial powers: Israel was no exception: Syria, Lebanon and Iraq were created at that time.