Bizarre phrase used by Andrew Marr in his interview with David Cameron on Sunday morning

From the Andrew Marr show transcript:

"ANDREW MARR: I'll look forward to that. Let's turn to nuclear power. Are you basically on all fours with the government when they, after their announcement about private companies being given the go-ahead to build more nuclear power stations? "


"Are you basically on all fours with the government...?"


What does that mean? Have you ever heard that expression before?