Prime Minister David Cameron says Britain's election campaign is on a knife edge as he rallies his Conservative party ahead of the close-fought race.

Cameron told a party conference Saturday that "this isn't any election. This is a high-stakes, high-risk election."

He continued, "this is a knife-edge election and can only be cut two ways: Conservative or Labour."

The campaign officially kicks off Monday, when Parliament is dissolved ahead of the May 7 vote.

Polls suggest no party will win a majority of seats.

Opposition Labour leader Ed Miliband launched his campaign Friday from the top of London's Orbit tower, promising to preserve the cash-strapped National Health Service.

Cameron also made the NHS a priority, vowing to ensure people have access to doctors and hospital services seven days a week.