The correct answer to this open question is the following.
The British changed their support in favor of the Jews because the British government though strategically and realized that a loyal ally in the Middle East region could be of many benefits for England.
Knowing that the Jewish people are wealthy, they supported them to establish Israel in the Palestinian territories with the support of the United States. This decision caused so much anger to Palestinians and has been the reason for many conflicts and wars in the Middle East region.
Basically, Jews Britain change its support in favor of Jews because they wanted to give some of Palestine's territory to them. If the Jews occupy the majority of that territory, it will be easier for the Britain if they wanted to expand their democratic influence towards the Middle East Region.
