In America the President and his cabinet , the Executive,are separated from the legislature. Whoever becomes President appoints his cabinet, which can not contain any members from either House of Congress. Politicians joining the cabinet have to resign from either the Senate or House of Representatives and positions are also open to to people outsde politics. So for example a General could become the Secretary of Defense. Finally the President's cabinet is not confirmed until approved by the Senate.
In this country our future PMs are chosen by their party and not the country at large and the cabinet and PM sit in the legislature or House of Commons.
Our system does not have a separation of power with the key disadvantage that with the Executive sitting in the House of Commons holding it to account is not so vigorous as it would be if it sat outside it.
If Biden wins his abilty to govern will be severely curtailed by the Republicans holding the Senate which, given the country is split virtually down the middle, between the Republicans and Democracts, is democracy in action.
A Separation of Power would improve our governance hence our third demand.