Israel wasn't founded by Britain. The UN is effectively what created Israel.
Britain acquired the region ("Mandatory Palestine") after WWI as a temporary measure to govern it until it was self-sustaining; that never happened, and in the wake of WWII, they mostly just wanted out of the situation and left the UN responsible. The UN voted on a partition plan - and the UK actually abstained from that vote.
Israel certainly wasn't founded by Britain, whose forces had simply abandoned the region after the Mandate expired in 1948, but the UN partition only set the stage for the eventual territorial bounds of Israel, as the partition plan was never actually implemented.
What cemented Israel's official modern territorial bounds were the 1949 Armistice Agreements following the 1948 Arab-Israeli War, which resulted in Israel controlling 60% of the land that was not originally defined for the Jewish State in the partition plan. According to the 1947 partition plan, Israel was not going to extend to Jerusalem, but the captured territory did extend to this point by the time of the 1949 armistice, as well as extending to most of the land border with Egypt which minimized the Gaza region's border with Egypt, and extending along Lebanon, which prevented the West Bank from sharing a border with Lebanon, as was intended in the partition plan.
Britain acquired the region ("Mandatory Palestine") after WWI as a temporary measure to govern it until it was self-sustaining; that never happened, and in the wake of WWII, they mostly just wanted out of the situation and left the UN responsible. The UN voted on a partition plan - and the UK actually abstained from that vote.
https://en.wikipedia.org/wiki/United_Nations_Partition_Plan_...