I'm not sure that's correct. The Conservatives have the most votes and the most seats, so arguably (and the other parties are arguing) they have a mandate, but they don't have the parliamentary arithmetic to form a government without some help. As I understand it, Gordon Brown is still the Prime Minister and has the right to try to form a new government. If he thinks he can command a majority in Parliament, he can carry on, until he's overturned by a vote of no confidence. However, he may decide he's got no chance, and resign. In either case the Conservatives could then try to form a government, and would themselves face the risk of a vote of no confidence. If it emerges that no one can command a working majority, we'll face another election.