There’s already a separate Arab state that was created out of the British Mandate - it’s called “Jordan” and it comprised about 7/8 of the land area of the Mandate. Any further division of the Jewish/Israeli side of that equation would be an even further cheating of the Jews/Israelis.
As for the viability of a 2nd state within the current borders of Israel - that is absurd, as such a state would be dedicated to the destruction of Israel itself, and the murder of as many of its citizens as possible. That’s simply a non-starter.
Oh, and haven’t the Brits f’ed up that part of the world enough? Shouldn’t they simply stay out?
Look at a map of the original U.N. Palestine partition plan from 1947. It’s easy to see how neither side would be happy with that highly irregular configuration of two separate jurisdictions.