The announcement to retain a large part of the coalition's spending by the Labour Party is significant because it shows a commitment to not drastically altering the current levels of public service funding. This decision implies a prioritization of maintaining existing services over implementing significant cuts or increases, which aligns with option B. Options A, C, and D introduce elements not directly supported by the passage, such as shifts in fiscal policy, government borrowing, or leadership changes, making them less accurate interpretations of the announcement's significance.